search strategy for research paper example

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How to write a search strategy for your systematic review

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Practical tips to write a search strategy for your systematic review

With a great review question and a clear set of eligibility criteria already mapped out, it’s now time to plan the search strategy. The medical literature is vast. Your team plans a thorough and methodical search, but you also know that resources and interest in the project are finite. At this stage it might feel like you have a mountain to climb.

The bottom line? You will have to sift through some irrelevant search results to find the studies that you need for your review. Capturing a proportion of irrelevant records in your search is necessary to ensure that it identifies as many relevant records as possible. This is the trade-off of precision versus sensitivity and, because systematic reviews aim to be as comprehensive as possible, it is best to favour sensitivity – more is more.

By now, the size of this task might be sounding alarm bells. The good news is that a range of techniques and web-based tools can help to make searching more efficient and save you time. We’ll look at some of them as we walk through the four main steps of searching for studies:

• Decide where to search
• Write and refine the search
• Run and record the search
• Manage the search results

Searching is a specialist discipline and the information given here is not intended to replace the advice of a skilled professional. Before we look at each of the steps in turn, the most important systematic reviewer pro-tip for searching is:

 Pro Tip – Talk to your librarian and do it early!

1. decide where to search .

It’s important to come up with a comprehensive list of sources to search so that you don’t miss anything potentially relevant. In clinical medicine, your first stop will likely be the databases MEDLINE , Embase , and CENTRAL . Depending on the subject of the review, it might also be appropriate to run the search in databases that cover specific geographical regions or specialist areas, such as traditional Chinese medicine.

In addition to these databases, you’ll also search for grey literature (essentially, research that was not published in journals). That’s because your search of bibliographic databases will not find relevant information if it is part of, for example:

• a trials register
• a study that is ongoing
• a thesis or dissertation
• a conference abstract.

Over-reliance on published data introduces bias in favour of positive results. Studies with positive results are more likely to be submitted to journals, published in journals, and therefore indexed in databases. This is publication bias and systematic reviews seek to minimise its effects by searching for grey literature.

2. Write and refine the search 

Search terms are derived from key concepts in the review question and from the inclusion and exclusion criteria that are specified in the protocol or research plan.

Keywords will be searched for in the title or abstract of the records in the database. They are often truncated (for example, a search for therap* to find therapy, therapies, therapist). They might also use wildcards to allow for spelling variants and plurals (for example, wom#n to find woman and women). The symbols used to perform truncation and wildcard searches vary by database.

Index terms  

Using index terms such as MeSH and Emtree in a search can improve its performance. Indexers with subject area expertise work through databases and tag each record with subject terms from a prespecified controlled vocabulary.

This indexing can save review teams a lot of time that would otherwise be spent sifting through irrelevant records. Using index terms in your search, for example, can help you find the records that are actually about the topic of interest (tagged with the index term) but ignore those that contain only a brief mention of it (not tagged with the index term).

Indexers assign terms based on a careful read of each study, rather than whether or not the study contains certain words. So the index terms enable the retrieval of relevant records that cannot be captured by a simple search for the keyword or phrase.

Use a combination

Relying solely on index terms is not advisable. Doing so could miss a relevant record that for some reason (indexer’s judgment, time lag between a record being listed in a database and being indexed) has not been tagged with an index term that would enable you to retrieve it. Good search strategies include both index terms and keywords.

Let’s see how this works in a real review! Figure 2 shows the search strategy for the review ‘Wheat flour fortification with iron and other micronutrients for reducing anaemia and improving iron status in populations’. This strategy combines index terms and keywords using the Boolean operators AND, OR, and NOT. OR is used first to reach as many records as possible before AND and NOT are used to narrow them down.

• Lines 1 and 2: contain MeSH terms (denoted by the initial capitals and the slash at the end).
• Line 3: contains truncated keywords (‘tw’ in this context is an instruction to search the title and abstract fields of the record).
• Line 4: combines the three previous lines using Boolean OR to broaden the search.
• Line 11: combines previous lines using Boolean AND to narrow the search.
• Lines 12 and 13: further narrow the search using Boolean NOT to exclude records of studies with no human subjects.

Writing a search strategy is an iterative process. A good plan is  to try out a new strategy and check that it has picked up the key studies that you would expect it to find based on your existing knowledge of the topic area. If it hasn’t, you can explore the reasons for this, revise the strategy, check it for errors, and try it again!

3. Run and record the search

Because of the different ways that individual databases are structured and indexed, a separate search strategy is needed for each database. This adds complexity to the search process, and it is important to keep a careful record of each search strategy as you run it. Search strategies can often be saved in the databases themselves, but it is a good idea to keep an offline copy as a back-up; Covidence allows you to store your search strategies online in your review settings.

The reporting of the search will be included in the methods section of your review and should follow the PRISMA guidelines. You can download a flow diagram from PRISMA’s website to help you log the number of records retrieved from the search and the subsequent decisions about the inclusion or exclusion of studies. The PRISMA-S extension provides guidance on reporting literature searches.

It is very important that search strategies are reproduced in their entirety (preferably using copy and paste to avoid typos) as part of the published review so that they can be studied and replicated by other researchers. Search strategies are often made available as an appendix because they are long and might otherwise interrupt the flow of the text in the methods section.

4. Manage the search results 

Once the search is done and you have recorded the process in enough detail to write up a thorough description in the methods section, you will move on to screening the results. This is an exciting stage in any review because it’s the first glimpse of what the search strategies have found. A large volume of results may be daunting but your search is very likely to have captured some irrelevant studies because of its high sensitivity, as we have already seen. Fortunately, it will be possible to exclude many of these irrelevant studies at the screening stage on the basis of the title and abstract alone 😅.

Search results from multiple databases can be collated in a single spreadsheet for screening. To benefit from process efficiencies, time-saving and easy collaboration with your team, you can import search results into a specialist tool such as Covidence. A key benefit of Covidence is that you can track decisions made about the inclusion or exclusion of studies in a simple workflow and resolve conflicting decisions quickly and transparently. Covidence currently supports three formats for file imports of search results:

• EndNote XML
• PubMed text format
• RIS text format

If you’d like to try this feature of Covidence but don’t have any data yet, you can download some ready-made sample data .

And you’re done!

There is a lot to think about when planning a search strategy. With practice, expert help, and the right tools your team can complete the search process with confidence.

This blog post is part of the Covidence series on how to write a systematic review.

Sign up for a free trial of Covidence today!

[1] Witt  KG, Hetrick  SE, Rajaram  G, Hazell  P, Taylor Salisbury  TL, Townsend  E, Hawton  K. Pharmacological interventions for self‐harm in adults . Cochrane Database of Systematic Reviews 2020, Issue 12. Art. No.: CD013669. DOI: 10.1002/14651858.CD013669.pub2. Accessed 02 February 2021

Laura Mellor. Portsmouth, UK

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Presenting a search strategy

Have you done a structured search related to a literature review or other work? Do you need to present how you found the articles you selected? Are you thinking about how you can present articles that you have found alongside the search, for example via a reference list to another article? Here you can see what information should be included in a search strategy presentation, and some examples of what it might look like.

What should be included in a search strategy presentation?

How can you present your search strategy.

• Strive to be as transparent as possible, it should preferably be possible for someone else to repeat your search and get the same result.
• In  the methods section you describe how you did: if you did test searches, how you found search words, if you searched with both free-text words and controlled subject headings.
• In the method section, you can also describe and report articles that you have found in other ways than via the database search, for example if you have found articles via a reference list to another article or by manual search .
• The complete search strategy is usually also presented in table form. The table can be added as an appendix to the work.
• In order for you to be able to present your search strategy, it is important that you save the search you have made , in some way. A tip is to cut and paste from the database's "Search history".
• It is also possible to create an account in the databases to save searches.

What should a search strategy presentation contain?

• The name of the database
• The date you did the search
• Which search terms you have used
• How you searched (quotes, especially fields, truncations, etc.)
• How you have combined your search terms
• If you have used any filter , or restriction (language, year, etc.)

Example of text in the methods section

The searches were conducted during June 2018 in the databases CINAHL, Web of Science and PubMed.

The Mesh terms identified for the PubMed search were adapted to corresponding terms in CINAHL. Every individual search term was supplemented with relevant free text terms. When appropriate, the free text terms have been truncated in order to include alternative word endings.

The search result was limited to articles that were written in English as well as articles published during the last ten years. The full search strategy is included as an appendix.

The database searches were complemented with manual review of the reference lists of relevant articles, which resulted in a few additional articles included in the study.

Examples from different databases

In the tables below we present searches in three different databases. In all databases we have used the topic " Patients' experience of day surgery ".

Example from CINAHL

MH = Exact Subject Heading

Example from PubMed

Example from web of science.

Guide for students: Structured literature reviews

A step-by-step guide aimed at Master's students undertaking a structured literature review as part of their Master's thesis. In this guide we will go through the different steps of a structured literature review and provide tips on how to make your search strategy more structured and extensive.

• How to conduct a systematic review
• Chapter 4 about Literature searching in the book Assessment of methods in health care - a handbook from the Swedish Agency for Health Technology Assessment and Assessment of Social Services.

Support in information searching

Are you looking for scientific articles or writing references and need advice? You can get help from our librarians. We offer both drop-in via Zoom and booked consultations.

Opening hours drop-in support in Zoom

If you would like us to get back to you, please submit your contact information in the form below along with your feeback.

Appendix 2: Example search strategy to identify studies from electronic databases  

The development of a search strategy is an iterative process: one attempt will rarely produce the final strategy. Strategies are usually built up from a series of test searches and discussions of the results of those searches among the review team.

The first step is to break down the review question to help guide the development of search terms, using a structure such as PICOS.

For example:

It is not necessary to include all of the PICOS concepts in the search strategy. It is preferable to search for those concepts that can be clearly defined and translated into search terms. Concepts that are poorly defined, not likely to be included in journal abstracts, or not indexed in a consistent way, will be difficult to identify from database searches. If this is the case, using a broader search and then sifting through the identified studies may be preferable. This may apply particularly to the outcome(s) of studies as these are frequently not referred to in either the title or abstract of a database record.

Search filters are tested and in some cases validated strategies that can be used in a named database to identify specific types of study. They usually consist of a series of database index terms relating to study type combined with free text terms describing the methods used in conducting that type of research. There are filters available that will, for example, reliably identify RCTs in MEDLINE and in EMBASE, but filters for use in other databases or to identify other study types are limited. The development and validation of filters to identify other study types, such as diagnostic accuracy studies and qualitative research, is ongoing. = 4) BSPSPopupOnMouseOver(event);" class="popupspot" >1 , = 4) BSPSPopupOnMouseOver(event);" class="popupspot" >2 , = 4) BSPSPopupOnMouseOver(event);" class="popupspot" >3 , = 4) BSPSPopupOnMouseOver(event);" class="popupspot" >4 A useful source of information about search filters is the website maintained by the InterTASC Information Specialists’ Subgroup www.york.ac.uk/inst/crd/intertasc/ which lists both published search filters and research on their development and use.

Once the concepts of the search have been determined, the next stage is to produce a list of synonyms, abbreviations and spelling variants which may be used by authors. Similar research is often described using very different terms. To reflect this variation, a search strategy will usually comprise both indexing terms (if the database has a thesaurus or controlled vocabulary) and ‘free text’ terms and synonyms (from the database record’s title and abstract) to ensure that as many relevant papers are retrieved as possible. For example, when searching MEDLINE for studies about myocardial infarction, the free text term “heart attack” should be used as well as the Medical Subject Heading (MeSH) term “Myocardial Infarction”. Identifying appropriate indexing terms can be done by searching for key papers and checking how they have been indexed, consulting clinical experts in the review team and advisory group, as well as by scanning the thesaurus for relevant terms.

When selecting free text terms to use in the strategy it is important to take account of alternative spellings (including US and British English variants), abbreviations, synonyms, geographical variation, and changes in terminology over time. Sometimes it can also be useful to search for common mis-spellings, for example “asprin” when you want to retrieve studies of aspirin.

The important thing is to compile imaginatively and to check the indexing terms used in known relevant publications. Once a list of potential search terms has been compiled for each of the concepts, the next stage is to identify relevant subject headings which have been used to describe the topic in the databases you plan to search. For example with post-operative infection the following Medical Subject Headings (MeSH) are available for use in MEDLINE:

Bacterial Infections

Postoperative Complications

Surgical Wound Infection

Prosthesis-Related Infections

Infection Control

Some of these terms are "high level" that encompass narrower or more specific terms. To capture these narrower terms, in those databases that offer the facility, it is possible to ‘explode’ the high level term and so search for many terms at once. The explosion facility within a database makes use of the hierarchical thesaurus. Using the command “exp Bacterial Infections/ ” in the OvidSP interface to MEDLINE will retrieve papers indexed with that term but will also automatically retrieve papers indexed with the narrower terms Bacteremia, Hemorrhagic Septicemia, Central Nervous System Bacterial Infections, etc. as displayed in the section of the MeSH below.

Bacterial Infections/

Hemorrhagic Septicemia

Central Nervous System Bacterial Infections

Endocarditis, Bacterial

Eye Infections, Bacterial

Fournier Gangrene

The subject headings should be added to the concept list relating to the post-operative infection concept so that a first test search strategy for MEDLINE includes a mixture of text terms and MeSH headings.

bacterial adj infect$.ti,ab.                                

(postoperative adj complication$ or post adj operative adj complication$).ti,ab.

surgical adj wound adj infection$.ti,ab.

prosthesis-related adj infection$.ti,ab.

hip adj replacement adj3 infection$.ti,ab.

sepsis.ti,ab.

Septic?emia.ti,ab.

infection adj control.ti,ab.

bacterial adj contamination.ti,ab.

exp Bacterial Infections/

exp Postoperative Complications/

Surgical Wound Infection/

Prosthesis-Related Infections/

exp Infection Control/

The search has been written for the OvidSP search interface to MEDLINE and has commands specific to that interface:

adj      Words have to appear next to each other. Also retrieves hyphenated words.

adj3    Words have to appear within 3 words of each other. Other numbers can be used as required.

$        Truncation symbol, for example ‘complication$’ retrieves 'complications' as well as 'complication'.

.ti,ab   Restricts the search to title and abstract fields, to avoid retrieving unexpected results from the subject headings.

EXP     Explode the subject heading, to retrieve more specific terms

/         MeSH heading.

?        O ptional wild card character used within, or at the end of, a search term to substitute for one or no characters. Useful for retrieving documents with British and American word variants.

Each database interface has its own unique set of commands and, information about these will be on the database help pages.

Once a series of concepts that reflect the PICOS elements have been compiled they are then combined using Boolean logic (AND, OR, NOT) to create a set of results which should contain articles relating to the topic in question. The AND operator is used to ensure that all the search terms must appear in the record, for example searching for “prostate AND cancer” retrieves all records which contain both the term prostate and the term cancer. AND is used to narrow down or focus a search.

OR is used to accumulate similar search terms and thus makes searches larger. Searching for “heparin OR warfarin” retrieves all records where either heparin or warfarin or both are found. It is best to use the OR operator to combine terms relating to the same concept (e.g. all the postoperative infection terms in the example above) before narrowing down a search using the AND operator with another set of terms.

NOT is used to exclude records from a search. For example, “acupuncture NOT asthma” will retrieve all records which contain the term acupuncture, but not those which also contain the word asthma. NOT should be used with great care because it may have a larger effect than anticipated; a record may well discuss both the concept of interest and the one to be excluded.

The combination of concepts using the Boolean operators might develop as follows (for MEDLINE using the OVIDSP interface):

1       Hip Joint/

2       Hip Prosthesis/

3       Acetabulum/

4       hip replacement$.ti,ab.

5       total-hip replacement$.ti,ab.

6       total joint replacement$.ti,ab.

7       hip surgery.ti,ab.

8       hip operation$.ti,ab.

9       (hip adj3 prosthe$).ti,ab.

10     (hip adj3 arthroplasty).ti,ab.

11     1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 or 9 or 10

12     exp Bacterial Infections/

13     exp Postoperative Complications/

14     Surgical Wound Infection/

14     Prosthesis-Related Infections/

16     Sepsis/

17     exp Anti-Infective Agents/

18     exp Infection Control/

19     exp Antibiotics/

20     Antibiotic Prophylaxis/

21       ((bacteri$ or wound$) adj2 (infect$ or contamin$)).ti,ab.

22       sepsis.ti,ab.

23       antibiotic$.ti,ab.

24       antimicrobial$.ti,ab.

25       anti-microbial$.ti,ab.

26       (anti$ adj infect$).ti,ab.

27       ultraclean.ti,ab.

28       hypersterile.ti,ab.

29       or/12-28

30       11 and 29

Sets 1 to 10 capture the concepts of hip replacement or hip surgery and are combined using OR to produce result set 11. Sets 12 to 28 capture the concepts of infection and infection prevention and are combined using OR to produce result set 29. The two sets of concepts are then combined to find the records which contain both concepts using AND to produce set 30.

The draft strategy can be tested on one database and the results checked by whether it retrieves papers that are already known to the team but were not used to develop the draft strategy. In addition, a small sample of the results of the test or scoping search can be examined by the review team to identify additional search terms (text words and indexing) or highlight potential limitations. The sample records need to be representative so bear in mind that the search results as output from the database will be listed in either alphabetical order by authors name, or by publication date or by date added to the database. Depending upon the complexity of the review topic, and consequently the search to be undertaken, this process may need to be repeated several times until an agreed strategy is formulated. If at all possible, the final search strategy should be peer reviewed to check for errors (spelling mistakes, incorrect use of operators, or failure to include relevant MeSH) that could reduce the recall of papers. = 4) BSPSPopupOnMouseOver(event);" class="popupspot" >5  

At this point, the searches using other databases and resources can begin. However, this does not mean that search iterations should necessarily stop. If new search terms are identified during the review process they should be incorporated into the strategy or supplementary searches should be carried out.

Converting a final strategy for use in other databases requires care. While free text terms can usually be re-used in other databases you will need to identify one or possibly more matching relevant thesaurus terms used by the other databases. Each database thesaurus is unique so this procedure should be undertaken for each database being searched. For example, if you are searching MEDLINE for papers about “pressure sores” you would use the MeSH term “pressure ulcer” while if you were searching EMBASE you would need to use the EMTREE term “decubitus”.

If the search interface is also different you will need to make appropriate changes to the search operators used in the strategy. For example, some database providers use ‘$’ as the truncation symbol, while other database providers use ‘*’.

Not all databases include an abstract in the record and if this is the case you may want to make your search strategy more sensitive as you are relying solely upon terms being identified in the title (and any indexing fields). You can do this by using more synonyms and broader terms.

In some cases databases with web interfaces have a restricted range of search options and if this is the case searchers need to adopt pragmatic approaches and use very simple searches. For example, if there are limited options for combining terms using Boolean operators such as AND an alternative approach may be to run a number of separate searches on the database in place of one longer search.

Literature Review: Developing a search strategy

• Traditional or narrative literature reviews
• Scoping Reviews
• Systematic literature reviews
• Annotated bibliography
• Keeping up to date with literature
• Finding a thesis
• Evaluating sources and critical appraisal of literature
• Managing and analysing your literature
• Further reading and resources

From research question to search strategy

Keeping a record of your search activity

Good search practice could involve keeping a search diary or document detailing your search activities (Phelps et. al. 2007, pp. 128-149), so that you can keep track of effective search terms, or to help others to reproduce your steps and get the same results. 

This record could be a document, table or spreadsheet with:

• The names of the sources you search and which provider you accessed them through - eg Medline (Ovid), Web of Science (Thomson Reuters). You should also include any other literature sources you used.
• how you searched (keyword and/or subject headings)
• which search terms you used (which words and phrases)
• any search techniques you employed (truncation, adjacency, etc)
• how you combined your search terms (AND/OR). Check out the Database Help guide for more tips on Boolean Searching.
• The number of search results from each source and each strategy used. This can be the evidence you need to prove a gap in the literature, and confirms the importance of your research question.

A search planner may help you to organise you thoughts prior to conducting your search. If you have any problems with organising your thoughts prior, during and after searching please contact your Library  Faculty Team   for individual help.

• Literature search - a librarian's handout to introduce tools, terms and techniques Created by Elsevier librarian, Katy Kavanagh Web, this document outlines tools, terms and techniques to think about when conducting a literature search
• Search planner

Literature search cycle

Have a search framework

Search frameworks are mnemonics which can help you focus your research question. They are also useful in helping you to identify the concepts and terms you will use in your literature search.

PICO is a search framework commonly used in the health sciences to focus clinical questions.  As an example, you work in an aged care facility and are interested in whether cranberry juice might help reduce the common occurrence of urinary tract infections.  The PICO framework would look like this:

Now that the issue has been broken up to its elements, it is easier to turn it into an answerable research question: “Does cranberry juice help reduce urinary tract infections in people living in aged care facilities?”

Other frameworks may be helpful, depending on your question and your field of interest. PICO can be adapted to PICOT (which adds T ime) or PICOS (which adds S tudy design), or PICOC (adding C ontext).

For qualitative questions you could use

• SPIDER : S ample,  P henomenon of  I nterest,  D esign,  E valuation,  R esearch type  

For questions about causes or risk,

• PEO : P opulation,  E xposure,  O utcomes

For evaluations of interventions or policies, 

• SPICE: S etting,  P opulation or  P erspective,  I ntervention,  C omparison,  E valuation or
• ECLIPSE: E xpectation,  C lient group,  L ocation,  I mpact,  P rofessionals,  SE rvice 

See the University of Notre Dame Australia’s examples of some of these frameworks. 

You can also try some PICO examples in the National Library of Medicine's PubMed training site: Using PICO to frame clinical questions.

Different search strategies

Contact Your Faculty Team Librarian

Faculty librarians are here to provide assistance to students, researchers and academic staff by providing expert searching advice, research and curriculum support.

• Faculty of Arts & Education team
• Faculty of Business, Justice & Behavioural Science team
• Faculty of Science team

Further reading

• << Previous: Annotated bibliography
• Next: Keeping up to date with literature >>
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• URL: https://libguides.csu.edu.au/review

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• Study and research support
• Literature searching

Literature searching explained

Develop a search strategy.

A search strategy is an organised structure of key terms used to search a database. The search strategy combines the key concepts of your search question in order to retrieve accurate results.

Your search strategy will account for all:

• possible search terms
• keywords and phrases
• truncated and wildcard variations of search terms
• subject headings (where applicable)

Each database works differently so you need to adapt your search strategy for each database. You may wish to develop a number of separate search strategies if your research covers several different areas.

It is a good idea to test your strategies and refine them after you have reviewed the search results.

How a search strategy looks in practice

Take a look at this example literature search in PsycINFO (PDF) about self-esteem.

The example shows the subject heading and keyword searches that have been carried out for each concept within our research question and how they have been combined using Boolean operators. It also shows where keyword techniques like truncation, wildcards and adjacency searching have been used.

Search strategy techniques

The next sections show some techniques you can use to develop your search strategy.

Skip straight to:

• Choosing search terms
• Searching with keywords
• Searching for exact phrases
• Using truncated and wildcard searches

Searching with subject headings

• Using Boolean logic

Citation searching

Choose search terms.

Concepts can be expressed in different ways eg “self-esteem” might be referred to as “self-worth”. Your aim is to consider each of your concepts and come up with a list of the different ways they could be expressed.

To find alternative keywords or phrases for your concepts try the following:

• Use a thesaurus to identify synonyms.
• Search for your concepts on a search engine like Google Scholar, scanning the results for alternative words and phrases.
• Examine relevant abstracts or articles for alternative words, phrases and subject headings (if the database uses subject headings).

When you've done this, you should have lists of words and phrases for each concept as in this completed PICO model (PDF) or this example concept map (PDF).

As you search and scan articles and abstracts, you may discover different key terms to enhance your search strategy.

Using truncation and wildcards can save you time and effort by finding alternative keywords.

Search with keywords

Keywords are free text words and phrases. Database search strategies use a combination of free text and subject headings (where applicable).

A keyword search usually looks for your search terms in the title and abstract of a reference. You may wish to search in title fields only if you want a small number of specific results.

Some databases will find the exact word or phrase, so make sure your spelling is accurate or you will miss references.

Search for the exact phrase

If you want words to appear next to each other in an exact phrase, use quotation marks, eg “self-esteem”.

Phrase searching decreases the number of results you get and makes your results more relevant. Most databases allow you to search for phrases, but check the database guide if you are unsure.

Truncation and wildcard searches

You can use truncated and wildcard searches to find variations of your search term. Truncation is useful for finding singular and plural forms of words and variant endings.

Many databases use an asterisk (*) as their truncation symbol. Check the database help section if you are not sure which symbol to use. For example, “therap*” will find therapy, therapies, therapist or therapists. A wildcard finds variant spellings of words. Use it to search for a single character, or no character.

Check the database help section to see which symbol to use as a wildcard.

Wildcards are useful for finding British and American spellings, for example: “behavio?r” in Medline will find both behaviour and behavior.

There are sometimes different symbols to find a variable single character. For example, in the Medline database, “wom#n” will find woman and also women.

Use adjacency searching for more accurate results

You can specify how close two words appear together in your search strategy. This can make your results more relevant; generally the closer two words appear to each other, the closer the relationship is between them.

Commands for adjacency searching differ among databases, so make sure you consult database guides.

In OvidSP databases (like Medline), searching for “physician ADJ3 relationship” will find both physician and relationship within two major words of each other, in any order. This finds more papers than "physician relationship".

Using this adjacency retrieves papers with phrases like "physician patient relationship", "patient physician relationship", "relationship of the physician to the patient" and so on.

Database subject headings are controlled vocabulary terms that a database uses to describe what an article is about.

Watch our 3-minute introduction to subject headings video . You can also  View the video using Microsoft Stream (link opens in a new window, available for University members only).

Using appropriate subject headings enhances your search and will help you to find more results on your topic. This is because subject headings find articles according to their subject, even if the article does not use your chosen key words.

You should combine both subject headings and keywords in your search strategy for each of the concepts you identify. This is particularly important if you are undertaking a systematic review or an in-depth piece of work

Subject headings may vary between databases, so you need to investigate each database separately to find the subject headings they use. For example, for Medline you can use MeSH (Medical Subject Headings) and for Embase you can use the EMTREE thesaurus.

SEARCH TIP: In Ovid databases, search for a known key paper by title, select the "complete reference" button to see which subject headings the database indexers have given that article, and consider adding relevant ones to your own search strategy.

Use Boolean logic to combine search terms

Boolean operators (AND, OR and NOT) allow you to try different combinations of search terms or subject headings.

Databases often show Boolean operators as buttons or drop-down menus that you can click to combine your search terms or results.

The main Boolean operators are:

OR is used to find articles that mention either of the topics you search for.

AND is used to find articles that mention both of the searched topics.

NOT excludes a search term or concept. It should be used with caution as you may inadvertently exclude relevant references.

For example, searching for “self-esteem NOT eating disorders” finds articles that mention self-esteem but removes any articles that mention eating disorders.

Citation searching is a method to find articles that have been cited by other publications.

Use citation searching (or cited reference searching) to:

• find out whether articles have been cited by other authors
• find more recent papers on the same or similar subject
• discover how a known idea or innovation has been confirmed, applied, improved, extended, or corrected
• help make your literature review more comprehensive.

You can use cited reference searching in:

• OvidSP databases
• Google Scholar
• Web of Science

Cited reference searching can complement your literature search. However be careful not to just look at papers that have been cited in isolation. A robust literature search is also needed to limit publication bias.

• Basics for GSIs
• Advancing Your Skills

Guiding Research Papers: Developing a Search Strategy

Tags: reading strategies , research skills , writing

Categories: Working with Student Writing

By Diane Matlock, English

A search strategy is a systematic plan for tracking down sources. No single search strategy works for every topic. For some topics, it may be appropriate to search for information in newspapers, magazines, and websites. For others, the best sources may be found in scholarly journals, books, and specialized reference works. Still other topics might be enhanced by field research, such as interviews, surveys, or direct observation.

Things to consider: You want to think about what will make the most interesting and effective evidence for your argument. Will you need primary sources, secondary sources, or both? Often what constitutes a primary or secondary source will depend on your purpose or field.

Primary and Secondary Sources

Primary sources enable the researcher to get as close as possible to what actually happened during a historical event or time period. A primary source reflects the individual viewpoint of a participant or observer. (Examples of primary sources include diaries, journals, speeches, interviews, letters, memos, manuscripts, memoirs, autobiographies, records of or information collected by government agencies, records of organizations, published materials written at the time about a particular event — books, magazine and journal articles, newspaper articles — photographs, audio recordings, moving pictures, video recordings, materials that document the attitudes and popular thought of a historical time period — public opinion polls, mass media, literature, film, popular fiction, textbooks — research data, artifacts.)

Some primary sources, such as diaries or letters, are original manuscripts which exist in only one place in the world. Others, such as newspaper articles or transcripts of speeches, exist in multiple copies but may be hard to find. You can look for reprinted primary sources.

A secondary source is a work that interprets or analyzes an historical event or phenomenon. It is generally at least one step removed from the event.

What kind of sources does the assignment require? How current do your sources need to be? Do you need to consult sources contemporary with an event or a person’s life? How many sources should you consult?

Finding Sources

One reason for doing research is to find information, data, and evidence bearing on a problem — the raw material of primary sources that become either support for your argument or the object of analytical scrutiny. The other reason for doing research is so you can place your argument in conversation with other scholars who have written on the topic — previous and contemporary scholars with whom you will agree or disagree. In other words, you need to understand the critical context for your argument. In addition, by reading secondary sources, you can examine how scholars in different disciplines use their sources.

To begin finding sources:

• Identify key participants, dates, and publications associated with your topic (for example, you can look at reports, newsletters, magazines, and pamphlets that were produced in conjunction with the event or developments you are researching)
• Search by subject (Library of Congress Library Subject Headings)
• Look up people, organizations, and agencies as authors
• Identify contemporary books from the era
• Use periodical and newspaper indexes from the time period
• Go to special collections of primary source material (look at the Bancroft materials online)
• Find popular fiction, movies, television from the time period
• Find public opinion polls from the period
• Use indexes to government documents
• Look at the bibliography of the secondary sources you examine

A Guide to Evidence Synthesis: 4. Write a Search Strategy

• Meet Our Team
• Our Published Reviews and Protocols
• What is Evidence Synthesis?
• Types of Evidence Synthesis
• Evidence Synthesis Across Disciplines
• Finding and Appraising Existing Systematic Reviews
• 0. Develop a Protocol
• 1. Draft your Research Question
• 2. Select Databases
• 3. Select Grey Literature Sources
• 4. Write a Search Strategy
• 5. Register a Protocol
• 6. Translate Search Strategies
• 7. Citation Management
• 8. Article Screening
• 9. Risk of Bias Assessment
• 10. Data Extraction
• 11. Synthesize, Map, or Describe the Results
• Evidence Synthesis Institute for Librarians
• Open Access Evidence Synthesis Resources

Video: Databases and search strategies (3:40 minutes)

Writing a Search Strategy

It is recommended that you work with a librarian to help you design comprehensive search strategies across a variety of databases. Writing a successful search strategy takes an intimate knowledge of bibliographic databases.  

Using Boolean logic is an important component of writing a search strategy: 

• "AND" narrows the search, e.g.  children AND exercise
• "OR" broadens the search, e.g.  (children OR adolescents) AND (exercise OR diet) 
• "NOT" excludes terms, e.g.  exercise NOT diet 
• "*" at the root of a word finds all forms of that word, e.g.  (child* OR adolescen*) AND (exercise* OR diet*)
• parentheses ensure all terms will be searched together as a set 
• quotations around a phrase searches that exact phrase, e.g.  (child* OR adolescen* OR "young adult*") 

Evidence Synthesis Search Strategy Examples

Agriculture Example: 

• Research question:  What are the strategies that farmer organizations use, and what impacts do those strategies have on small-scale producers in Sub Saharan Africa and India? 
• Key concepts from the question combined with AND:  (farmer organizations) AND (Sub-Saharan Africa OR India) 
• Protocol and search strategies for this question in CAB Abstracts, Scopus, EconLit, and grey literature
• Published scoping review for this question

Nutrition Example: 

• Research question:  What are the health benefits and safety of folic acid fortification of wheat and maize flour (i.e. alone or in combination with other micronutrients) on folate status and health outcomes in the overall population, compared to wheat or maize flour without folic acid (or no intervention)? 
• Key concepts from the question combined with AND:  (folic acid) AND (fortification) 
• Protocol on PROSPERO
• Published systematic review for this question with search strategies used in 14 databases

Search Strategy Template and Filters

• Human Studies Filter
• Randomized Controlled Trial Filters
• Other Methodology Search Filters

If you want to exclude animal studies from your search results, you may add a "human studies filter" to the end of your search strategy. This approach works best with databases that use Medical Subject Headings (MeSH) or other controlled vocabulary.

See Appendix 2 at the end of this published search strategy for an example of a human studies filter in a MEDLINE(Ovid) search strategy.

Line 13 searches for all animal studies, and then line 14 searches for only the full search results in line 12, NOT including any of the animal studies from line 13 (#12 NOT #13).

Add the following lines to the end of your search strategy to filter for randomized controlled trials. These are "validated search filters" meaning they have been tested for sensitivity and specificity, and the results of those tests have been published as a scientific article. The ISSG Search Filters Resource provides validated search filters for many other study design types. 

Highly Sensitive MEDLINE (via PubMed) Filter from Cochrane  

(randomized controlled trial [pt] OR controlled clinical trial [pt] OR randomized [tiab] OR placebo [tiab] OR drug therapy [sh] OR randomly [tiab] OR trial [tiab] OR groups [tiab])

Highly Sensitive MEDLINE (OVID) Filter from Cochrane 

((randomized controlled trial.pt. or controlled clinical trial.pt. or randomized.ab. or placebo.ab. or drug therapy.fs. or randomly.ab. or trial.ab. or groups.ab.) not (exp animals/ not humans.sh.)) ​

CINAHL Filter from Cochrane 

TX allocat* random* OR (MH "Quantitative Studies") OR (MH "Placebos") OR TX placebo* OR TX random* allocat* OR (MH "Random Assignment") OR TX randomi* control* trial* OR TX ( (singl* n1 blind*) OR (singl* n1 mask*) ) OR TX ( (doubl* n1 blind*) OR (doubl* n1 mask*) ) OR TX ( (tripl* n1 blind*) OR (tripl* n1 mask*) ) OR TX ( (trebl* n1 blind*) OR (trebl* n1 mask*) ) OR TX clinic* n1 trial* OR PT Clinical trial OR (MH "Clinical Trials+")

PsycINFO Filter from ProQuest:

SU.EXACT("Treatment Effectiveness Evaluation") OR SU.EXACT.EXPLODE("Treatment Outcomes") OR SU.EXACT("Placebo") OR SU.EXACT("Followup Studies") OR placebo* OR random* OR "comparative stud*" OR  clinical NEAR/3 trial* OR research NEAR/3 design OR evaluat* NEAR/3 stud* OR prospectiv* NEAR/3 stud* OR (singl* OR doubl* OR trebl* OR tripl*) NEAR/3 (blind* OR mask*)

Web Of Science (WoS) Filter from University of Alberta - Not Validated

TS= clinical trial* OR TS=research design OR TS=comparative stud* OR TS=evaluation stud* OR TS=controlled trial* OR TS=follow-up stud* OR TS=prospective stud* OR TS=random* OR TS=placebo* OR TS=(single blind*) OR TS=(double blind*)

Scopus Filter from Children's Mercy Kansas City

 Copy/paste into 'advanced search':

TITLE-ABS-KEY((clinic* w/1 trial*) OR (randomi* w/1 control*) OR (randomi* w/2 trial*) OR (random* w/1 assign*) OR (random* w/1 allocat*) OR (control* w/1 clinic*) OR (control* w/1 trial) OR placebo* OR (Quantitat* w/1 Stud*) OR (control* w/1 stud*) OR (randomi* w/1 stud*) OR (singl* w/1 blind*) or (singl* w/1 mask*) OR (doubl* w/1 blind*) OR (doubl* w/1 mask*) OR (tripl* w/1 blind*) OR (tripl* w/1 mask*) OR (trebl* w/1 blind*) OR (trebl* w/1 mask*)) AND NOT (SRCTYPE(b) OR SRCTYPE(k) OR SRCTYPE(p) OR SRCTYPE(r) OR SRCTYPE(d) OR DOCTYPE(ab) OR DOCTYPE(bk) OR DOCTYPE(ch) OR DOCTYPE(bz) OR DOCTYPE(cr) OR DOCTYPE(ed) OR DOCTYPE(er) OR DOCTYPE(le) OR DOCTYPE(no) OR DOCTYPE(pr) OR DOCTYPE(rp) OR DOCTYPE(re) OR DOCTYPE(sh))

Sources and more information:

• Cochrane Handbook for Systematic Reviews of Interventions
• Cochrane RCT Filters for Different Databases
• American University of Beirut University Libraries Search Filters / Hedges
• Methodology Search Filters by Study Design Filters for RCTs, CCTs, Non-randomized/observational designs, and tests of diagnostic accuracy. Source: Countway Library of Medicine. (2019). Systematic Reviews and Meta Analysis: Methodology Filters.
• American University of Beirut University Libraries Search Filters Filters for RCTs, GUIDELINEs, systematic reviews, qualitative studies, etc. Source: American University of Beirut University Libraries. (2019). Systematic Reviews: Search Filters / Hedges.

Pre-generated queries in Scopus for the UN Sustainable Development Goals

Pre-written SDG search strategies available in Scopus 

Scopus, a database of multidisciplinary research, provides pre-written search strategies to capture articles on topics about each of the 17 United Nations Sustainable Development Goals  (SDGs). To access these SDG search strategies in Scopus: 

• Click on "Advanced Document Search" 
• At the bottom of the right-hand column, click on "pre-generated queries." When you click on one of the 17 SDGs, a search strategy for that SDG will populate in the search field in Scopus syntax.  

More about the Sustainable Development Goals: 

" The 2030 Agenda for Sustainable Development,  adopted by all United Nations Member States in 2015, provides a shared blueprint for peace and prosperity for people and the planet, now and into the future. At its heart are the 17 Sustainable Development Goals (SDGs), which are an urgent call for action by all countries - developed and developing - in a global partnership. They recognize that ending poverty and other deprivations must go hand-in-hand with strategies that improve health and education, reduce inequality, and spur economic growth – all while tackling climate change and working to preserve our oceans and forests."

Source:  https://sdgs.un.org/goals 

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• Last Updated: Nov 2, 2023 11:42 AM
• URL: https://guides.library.cornell.edu/evidence-synthesis

How to Write a Research Paper

• Formulate Questions/Thesis
• Identify Keywords
• Find Background Info

Search Strategies

• Dissertations
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• Statistics This link opens in a new window
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• Creative Commons
• Cite This link opens in a new window
• Quote, Paraphrase, Summarize

Boolean Operators

Boolean operators (AND, OR, and NOT) are used to connect keywords and concepts when searching.

• Boil your topic down to the most important words .  Ignore superfluous words like in, the, of, with, against, affect, impact.  Begin with a keyword search. 
• Put each "different piece" of your topic in a separate search box, if available.  Using the topic of criticism of Van Gogh's Starry Night as an example below, each different piece of the topic is entered on a separate line.  Synonyms for the pieces are connected by OR--and kept on the same line--as seen below with criticize...

•  Too many results?  Focus your search by searching for your keywords in the ABSTRACT field or the TITLE field.  Click on the All - Smart Search to select  the abstract or title field.  Or focus your search by using "an exact phrase" search.
• Too few results?  Think of synonyms.  Add synonyms to your search--using OR-- and keep your synonyms all on the same line . 
• Increase your results by removing the least important "piece" of your search while still retaining the "essence" of your search (in the case above, it might be Van Gogh). 
• Still no results?  Broaden your search slightly.  Can't find specific criticism on the Starry Night?  Look for criticism of Van Gogh--within these articles/books, you'll find criticism of Starry Night.  Still no luck?  Try a different journal article database.
• When reviewing your results, look for relevant "subject" or "descriptor" words.  Find subject terms either on the results page, or at the end of individual records.  Write down relevant subject terms that you find.  
• Go back to the search screen and using the subject terms you discovered, search your subject terms in the subject or descriptor field.  Subject terms are gold threads--they will almost always lead you to the most relevant results.
• Be sure to take advantage of:
• Boolean connectors (AND, OR, NOT)
• Exact phrase searching -- "starry night" 
• Field searches (search within the title, abstract, or subject fields)

• No full-text?  Use the L ooking for Full-Text (a Get It link will appear if the full-text links fails) OR Request from LVC Tipasa link to receive a copy of the article or book from another library.

If your initial search query does not produce the desired results, try:

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Literature Search Basics

Develop a search strategy.

• Define your search
• Decide where to search

What is a search strategy

Advanced search tips.

• Track and save your search
• Class Recording: Writing an Effective Narrative Review
• A search strategy includes  a combination of keywords, subject headings, and limiters (language, date, publication type, etc.)
• A search strategy should be planned out and practiced before executing the final search in a database.
• A search strategy and search results should be documented throughout the searching process.

What is a search strategy?

A search strategy is an organized combination of keywords, phrases, subject headings, and limiters used to search a database.

Your search strategy will include:

• keywords 
• boolean operators
• variations of search terms (synonyms, suffixes)
• subject headings 

Your search strategy  may  include:

• truncation (where applicable)
• phrases (where applicable)
• limiters (date, language, age, publication type, etc.)

A search strategy usually requires several iterations. You will need to test the strategy along the way to ensure that you are finding relevant articles. It's also a good idea to review your search strategy with your co-authors. They may have ideas about terms or concepts you may have missed.

Additionally, each database you search is developed differently. You will need to adjust your strategy for each database your search.  For instance, Embase is a European database, many of the medical terms are slightly different than those used in MEDLINE and PubMed.

Choose search terms

Start by writing down as many terms as you can think of that relate to your question. You might try  cited reference searching  to find a few good articles that you can review for relevant terms.

Remember than most terms or  concepts can be expressed in different ways.  A few things to consider:

• synonyms: "cancer" may be referred to as "neoplasms", "tumors", or "malignancy"
• abbreviations: spell out the word instead of abbreviating
• generic vs. trade names of drugs

Search for the exact phrase

If you want words to appear next to each other in an exact phrase, use quotation marks, eg “self-esteem”.

Phrase searching decreases the number of results you get. Most databases allow you to search for phrases, but check the database guide if you are unsure.

Truncation and wildcards

Many databases use an asterisk (*) as their truncation symbol  to find various word endings like singulars and plurals.  Check the database help section if you are not sure which symbol to use. 

"Therap*"

retrieves: therapy, therapies, therapist or therapists.

Use a wildcard (?) to find different spellings like British and American spellings.

"Behavio?r" retrieves behaviour and behavior.

Searching with subject headings

Database subject headings are controlled vocabulary terms that a database uses to describe what an article is about.

Using appropriate subject headings enhances your search and will help you to find more results on your topic. This is because subject headings find articles according to their subject, even if the article does not use your chosen key words.

You should combine both subject headings and keywords in your search strategy for each of the concepts you identify. This is particularly important if you are undertaking a systematic review or an in-depth piece of work

Subject headings may vary between databases, so you need to investigate each database separately to find the subject headings they use. For example, for MEDLINE you can use MeSH (Medical Subject Headings) and for Embase you can use the EMTREE thesaurus.

SEARCH TIP:  In Ovid databases, search for a known key paper by title, select the "complete reference" button to see which subject headings the database indexers have given that article, and consider adding relevant ones to your own search strategy.

Use Boolean logic to combine search terms

Boolean operators (AND, OR and NOT) allow you to try different combinations of search terms or subject headings.

Databases often show Boolean operators as buttons or drop-down menus that you can click to combine your search terms or results.

The main Boolean operators are:

OR is used to find articles that mention  either  of the topics you search for.

AND is used to find articles that mention  both  of the searched topics.

NOT excludes a search term or concept. It should be used with caution as you may inadvertently exclude relevant references.

For example, searching for “self-esteem NOT eating disorders” finds articles that mention self-esteem but removes any articles that mention eating disorders.

Adjacency searching 

Use adjacency operators to search by phrase or with two or more words in relation to one another. A djacency searching commands differ among databases. Check the database help section if you are not sure which searching commands to use. 

In Ovid Medline

"breast ADJ3 cancer" finds the word breast within three words of cancer, in any order.

This includes breast cancer or cancer of the breast.

Cited Reference Searching

Cited reference searching is a method to find articles that have been cited by other publications. 

Use cited reference searching to:

• find keywords or terms you may need to include in your search strategy
• find pivotal papers the same or similar subject area
• find pivotal authors in the same or similar subject area
• track how a topic has developed over time

Cited reference searching is available through these tools:

• Web of Science
• GoogleScholar
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Search examples

On this page we provide examples of database searches from selected disciplines, simply to give you an idea of what you might encounter. When it comes to literature searching, one size does not fit all, and not everyone will find examples of exactly the kind of search they need to do. 

You should always adapt your searching to your information needs, the standards of your discipline, and the particulars of your project.

Remember too that literature searches usually need to be revised and repeated several times in the course of your work towards the PhD. An exception to this rule is when you prepare a systematic review . For a systematic review, an end point to the search must be defined so that the review will be limited to the literature available at a given point in time. 

On this page you will find example searches from medicine, biology, psychology, education, and one systematic search including a thorough introduction to the method. 

Research question:   The effectiveness of light therapy interventions to treat winter depression.

Database:  PubMed (Medline). Relevant in biomedicine, life sciences and social sciences.  

Divide your search into several steps and combine results afterwards. When searching literature in medicine and health, make use of subject headings in the MeSH thesaurus.

Step 1:  Searching for “winter depression”

The MeSH term for this is seasonal affective disorder. In Scandinavia, this condition is commonly called winter depression, which is mentioned in a few abstracts. The terms are combined with OR to retrieve articles in which either is mentioned. The list below shows search terms[field searched] and numbers of results. Searches are marked with the hash symbol ( # ) in PubMed.

Search 1: seasonal affective disorder[MeSH Terms] 1215 Search 2: seasonal affective disorder[Title/Abstract] 1264 Search 3: winter depression[Title/Abstract] 281 Search 4: #1 OR #2 OR #3 1744

Step 2:  Searching for “light therapy interventions”

The correct MeSH term for light therapy intervention is phototherapy and this is combined with light therapy in the title and abstract as a synonym. Additional searches for the terms in titles or abstracts here add a few relevant articles. They are all combined with OR to retrieve articles in which either term is mentioned.

Search 5: phototherapy[MeSH Terms] 41845 Search 6: phototherapy[Title/Abstract] 8512 Search 7: light therapy[Title/Abstract] 2093 Search 8: #5 OR #6 OR #7 45782

Step 3:  Combining search results

Finally, both sets of terms are combined with AND. This will retrieve a combination of the words above.

Search 9: #4 AND #8 771

Step 4:  Limiting search results

Now you have 771 references to articles concerning your search terms. If you want to further decrease that number, you can limit the result, for example by study design. Reviews summarise previous research and may be a good starting point. In this case, by limiting to reviews, you will retreive 162 studies.

Search 10: (# 9) Filters: Review 162

In addition, limiting by year of publication will reduce the number of studies even further. There are 35 reviews published in the last ten years.

Search 11: (# 9) Filters: Review; published in the last ten years 35

For an initial check on the relevance of the retrieved documents, browse titles, year of publication, contributing authors and the journals involved. Keep revising your search strategy and also consider setting up an alert. As no database is exhaustive, consider including searches in other databases. 

Research question:   Symbiotic relationships between Lepiotaceaean fungi and leaf-cutter ants.

Database:  BIOSIS Previews, which is a part of Web of Science. Relevant for the life sciences.

Divide your search into several steps; search separately for relevant keywords according to research topic; combine and refine afterwards.

Step 1:  Searching for  leaf cutter ants  and  Lepiotaceaea fungi

Make sure to include various spellings and relevant synonyms of a search term. In this case, Latin names and common names are combined in a Boolean OR search. Add a wildcard   (here *) to the stem of a word to include all forms. In BIOSIS, searching by topic means searching by title, abstract or keywords. The list below shows search terms and number of results in parentheses.

Search 1: Topic=(Atta OR Acromyrmex OR (leaf cutt* ant*) OR (leafcutt* ant*)) (1529) Search 2: Topic=(fungus OR fungi OR lepiotaceae*) (488401)

Step 2:  Combining search results

Go to your search history and combine the previous two searches with the Boolean operator AND. Searches are marked with the hash symbol (#) in BIOSIS.

Search 3: #1 AND #2 (385)

Step 3:  Refine results to type of work

The left panel in the result list of the search interface lets you refine your search. Reviews summarise previous research and may be a good starting point. Choose Literature Types and tick off Literature Review if you would like to start with the eight papers retrieved in our example.

Search 4: Refined by: Literature Types=(LITERATURE REVIEW) (8)

Conclusion:

For our topic  Symbiotic relationships between Lepiotaceae fungi and leaf-cutter ants , a total of 385 documents were retrieved in BIOSIS(Step 2).

While it is tempting to include a third search concept, symbiosis, this would exclude the documents dealing with symbiosis without mentioning it in the title, abstract or keywords. If a paper is about both fungi and ants, it is also likely to relate to symbiosis. In other words, this might increase the specificity of the search, but at the same time reduce the sensitivity.

For an initial check on the relevance of the retrieved documents, try browsing titles, year of publication, contributing authors and the journals involved. As no database is exhaustive, consider including searches in other databases. Keep revising your search strategy and also consider setting up an alert.

Research question:   The impact of having divorced parents on self-esteem in adolescents.

Database:  PsycINFO (Ovid). Relevant for psychology, health sciences, social sciences and education.

Divide your search into several steps. Identify the main concepts in your research question and search separately for relevant keywords for each concept. In this example, the main concepts are self-esteem, adolescents, and divorced parents. Individual searches for main concepts and synonyms / alternative spellings of search terms within a main concept are combined. You can then consider using various possibilities to refine your search result.

Step 1:  Searching for “self-esteem”

Make sure to include various spellings and relevant synonyms of a search term or search concept. You might want to consider whether the concepts “self-respect” and/or “self-confidence” ought to be included. Many databases treat the spelling alternatives “self esteem” and “self-esteem” identically. It is recommended that you check if both alternatives need to be included. It is also easy to test whether a search term consisting of more than one word should be delimited with quotation marks. Check the thesaurus  for possible subject headings that match your main concepts well enough to be included as keywords. In PsycINFO (on Ovid), a subject heading search will be marked with a slash (/) in the search history. The Search History in the database presents the individual searches representing the main concept, “self-esteem”, and you combine them using the Boolean operator OR. The list below shows spelling variants of “self-esteem”, field searched (ti,ab = title, abstract), and the numbers of results in parentheses.

Search 1: self-esteem.ti,ab. (41932) Search 2: selfesteem.ti,ab. (83) Search 3: self esteem/ (24471) Search 4: Search 1 OR Search 2 OR Search 3 (46039)

Step 2:  Searching for  adolescents

Truncating  after the ‘n’ in adolescen* will include adolescent, adolescents and adolescence. Truncating after the ‘n’ in teen* will include teens, teen-ager/-s and teenager/-s. You might also want to consider including the search terms youth*, “young people” and student*.

Search 5: adolescen*.ti,ab. (220286) Search 6: teen*.ti,ab. (20825) Search 7: adolescent development/ (45687) Search 8: Search 5 OR Search 6 or Search 7 (236189)

Step 3:  Searching for  divorced parents

Truncating after the ‘e’ in divorce* will include divorced (which will also identify “divorced parents” and “parents who are divorced”). Including terms other than divorce might be a good idea if it is umimportant that the parents were married before they broke up. PsycINFO allows for truncation within a compound search term, such as “parent* breakup” which will include parental breakup, parents breakup and parent breakup. The searches representing the concept of “divorce” are combined with OR (Search 14).

Search 9: divorce*.ti,ab. (16833) Search 10: “broken home*”.ti,ab. (528) Search 11: “parent* breakup”.ti,ab. (10) Search 12: “parent* break-up”.ti,ab. (15) Search 13: divorce/ (8244) Search 14: Search 9 OR Search 10 OR Search 11 OR Search 12 OR Search 13 (18194)

Step 4:  Combining search results

Go to your search history and combine previous searches with the Boolean operator AND.

Search 15: Search 4 AND Search 8 AND Search 14 (106)

Step 5:  Refining results to type of work

You can refine your search by choosing Additional Limits. If, for example, you want to identify the reviews among your search results, choose the Methodology box and mark the following options: 0800 Literature Review, 0830 Systematic Review, 1200 Meta Analysis and 1300 Metasynthesis. Limiting our research question by these types of applied methodology retrieves 3 documents.

Search 16: limit 15 to (0800 literature review OR 0830 systematic review OR 1200 meta analysis OR 1300 metasynthesis) (3)

For our research question “The impact of having divorced parents on self-esteem in adolescents”, a total of 106 documents were retrieved in PsycINFO (Step 4) . Keep revising your search strategy and consider setting up an alert. As no database is exhaustive, consider including searches in other databases.

Research question:   What is the teacher's role in supporting play in the kindergarten?

Database:  ERIC (Ebsco). International database on education literature and resources.

Divide your research question into several concepts, search for them separately, and make use of the search history to combine results afterwards. When searching for literature in a database that has its own thesaurus , remember to make use of relevant thesaurus terms, also called subject headings.

Step 1:  Searching for “kindergarten teacher”

When typing "kindergarten teacher" into the thesaurus, we learn that "Preschool teachers" is the correct subject heading. Therefore we first apply that in the field Descriptors [exact] (DE).

When searching the fields Title and Abstract (and Author keywords when available) - both “Kindergarten” and “Kindergarden” can be used, as well as “Preschool”, “Daycare”, “Child care center” and “Nursery”.

In search 2, each of these terms is combined with the Boolean operator OR, to retrieve articles where either is mentioned. They are then combined with a proximity operator (N8), saying that the word “teacher” should be found within 8 words' distance. All the words end with an asterisk, opening for any character following. For instance, nurser* includes nurser y and nurser ies . The same search string is used in the fields Title (TI), Abstract (AB), and Keywords (KW). Each string is enclosed within parentheses, which are combined with OR.

Then we combine Search 1 and Search 2 with OR. 

Step 2:  Searching for “Play”

The thesaurus term is “Play”. Other terms like: Role Play, Playground activities may be considered, but are not included here.

We would also like to find articles with “Play” in the title, abstract or author keywords. We add an asterisk (*) to include different variations of the word (play s , play ed , play ing ), and again we search for the same thing in different fields, which we then combine with OR.

Now you have 1755 references to articles concerning your search terms. If you want to decrease that number, you can limit , for example by study design or year of  publication. Limiting to references from 2018–2021 will retrieve 292 studies.

For an initial check on the relevance of the retrieved documents, browse titles and abstracts. Look for any other relevant search terms. Keep revising your search. When you are satisfied with the search, consider saving it and setting up an alert. As no database is exhaustive, also consider performing searches in other databases.

Systematic searching

When working with a systematic review , the search is an important part of the method. The search will provide the data set for the investigation undertaken in the review. 

Systematic searching can be useful even if you do not plan to write a complete, stand-alone review. Researchers' interest in using this method seems to be on the rise in fields that have less of a tradition for systematic searches and systematic reviews than do medicine and nursing, for example.

To perform a systematic search, you do not need to learn special search techniques. If you plan to publish the search, however, it must be documented in compliance with one of the established standards and/or your publisher's guidelines. It is a good idea to let the relevant standard structure your search process from the outset. When you publish a stand-alone review, documentation of the search process is published with it. 

In the following, we provide advice for different steps in the process of searching in preparation for writing systematic reviews. We illustrate this with examples of how you can articulate and build search strategies and adapt them for use in different databases, and we suggest ways of documenting searches in dissertations and journal articles. 

Prepare your search

Preparing the search is crucial, as this will be the foundation for further work.

• Identify the main elements of your research question Defining the elements from your research question that you want to include in the search will help you choose search terms effectively. Too few elements will result in an unspecific search and many irrelevant hits. Too many elements can make it difficult to find anything at all or may lead to a biased selection of studies.
• Make a choice of relevant and accessible databases to search Your library may subscribe to relevant databases that you are not aware of. Choose as many relevant ones as you need. Even though there may be overlap in the search results, you will probably gain additional references. Consult the manuals of the chosen databases. Here you will find information about such advanced search options as truncation symbols, Boolean operators and syntax in each database.
• Grey literature ‘Grey literature’ is a common name for information or publications not appearing in regular channels for scholarly communication (research articles and books). These publications are typically from research institutes or government bodies, and are often not registered (or indexed) in research databases. The publications can be located on institutional websites, in library catalogues and discovery systems, or in designated databases for grey literature.
• Strategies for tracing references To be as exhaustive as possible, making sure all relevant literature is included, the reference lists of relevant studies should also be traced . 
• Find search terms To capture all previous research, use an exhaustive set of search terms. Include synonyms and use thesauruses and the subject headings relevant to the selected databases for your overall search.
• Unpublished material  In addition to databases of published research you can find databases of pre-registered projects of different kinds. If you are preparing a systematic review in a medical field, you can make use of one of several databases of registered clinical trials to discover unpublished results from completed trials. 

In searching, we distinguish between text words and subject headings, which are in different searchable fields of a reference. Text words (also called free text) are the author’s own written words that appear in the title and abstract. Subject headings describe the content of an article and are added by the database providers; these are often standardised.

Strategies for finding search terms

• Off the top of your head. If you know the field, you already know several relevant terms.
• Scan journal articles. A good exercise is to analyse the text of articles on the topic to identify common terms used in the field. Check for words in the title, abstract, author’s keywords and the text.
• In addition, do some trial searches. See if any unexpected but relevant terms appear.

This example shows subject headings in Medline (which uses MeSH) and Embase (which uses Emtree), using different terms to describe the same concepts.

• Look up relevant references in databases and see what subject headings they are indexed with. Check the same reference in databases with different thesauruses.
• Take advantage of others’ published search strategies. Search strategies are often included in review articles. Search for reviews on your topic or parts of it, and see if there is anything you can use. Systematic reviews from the Cochrane Collaboration usually present their full search strategies in an appendix to their published review.
• Text analysis programs. There are various text analysers available online that can help you discover even more search terms. Reference managers such as Endnote also generate a term list based on library references, which can be useful.

Language, publication year, demography and methodology filters

If your research question allows for limitations, these may be applied in the literature search as well. Most databases allow limitations by year, language, demography, research design, etc. Consider using these for enhanced precision.

Test and revise your search

If you have a set of key articles on your topic, use them to test your search. First, check whether they are indexed in the database, then check whether they come up in your search. If they are not included in the search, try to find out why and revise your strategy. Missed search terms? Too narrow limitations?

Part of the process of searching is to revise your search several times. By including or excluding terms and testing your search, you will end up with what best suits your research question.

Peer review of search strategy

When critically appraising a systematic review, it is important to determine whether all relevant key studies have been included. This can be assessed by evaluating the literature search, that is, the sources and search terms used. Similarly, you can have a colleague or information specialist peer-review your search strategy during the review process to help improve the quality of the review. Others might identify missed terminology, syntax errors and other mistakes which are easily overlooked.

The  PRESS checklist (Peer Review of Electronic Search Strategies ) has been developed to identify elements of accuracy of literature searches.

Example searches

The precise way to build up a search strategy will depend on the researcher and on the database. In the following we present an example of how the process of developing a search strategy might look and how the literature searches will look in different databases.

Our research question is: Does exposure to smoke from e-cigarettes increase the risk of obstructive lung disease?

For this, we will limit our search to PubMed, Embase and Web of Science. In a real-life systematic review on the topic, we would search more databases.

The main elements of this question are

• electronic cigarettes
• obstructive lung diseases
• second-hand smoking

To search as thoroughly as possible, we need all the terms describing these concepts. To systematise this work, all the words are organised in the table below.

• The most obvious search terms here are words from our research question, and they will be the starting point for the search. These words will be used as text words both in the singular and plural, truncated with an asterisk * in the table.
• Other natural language words and abbreviations should also be included as text words.
• We then search the MeSH database for relevant MeSH-terms and Embase for Emtree terms. These subject headings are also used as text words, as subject headings and text words are placed in different fields of a reference.
• By searching and surfing the databases, we can identify additional search terms. In this example, when searching for electronic cigarettes we stumbled upon an article about 'electronic nicotine delivery systems', which was a new term for us. As it is the ‘electronic nicotine’ that is the core of our question and not the ‘delivery system’, we chose to use only ‘electronic nicotine’.
• ‘Vaporizers’ is also a common term used for the smoking equipment. However, as vaporizers are also used in other contexts (e.g. inhaling medications), it is important to relate the term to smoking or nicotine to prevent retrieval of irrelevant references. Therefore, smoking/nicotine must be combined within brackets/parentheses with AND, or their respective search lines can be combined with AND.
• By combining text words and subject terms on the same concept with OR you will get either of the variations and probably retrieve all literature concerning that concept.
• Then combine all search terms across concepts with AND.
• Our search terms are then applied in the chosen databases. The database syntax is considered and we adapt the search strategy for each specific database.
• As electronic cigarettes are quite a new phenomenon, we have not applied any publication limitations. The topic will limit itself by date.
• We have not applied language filters in order to retrieve all literature on the topic.

The following searches in PubMed, Embase Ovid and Web of Science might have these outcomes: 

Example PubMed search strategy

Example embase ovid search strategy.

Note: The / indicates a subject heading from Emtree and .tw. indicates text words.

Example Web of Science search strategy

Note: Web of Science does not have a subject heading index; therefore all search terms are text words.

Processing the search result

There are 235 retrieved references in these searches. As this is a relatively small number, we chose not to limit our search further. Had the number of hits been high, a relevant step would be to add a methodological filter to narrow our search to observational studies.

While searching multiple databases, importing the result to a reference management program can help you create an efficient workflow. The reference manager can remove duplicate references, help you sort relevant references and organise your further work.

• The three databases have a total of 235 references (respectively 123, 77 and 35).
• After automatic deduplication in Endnote, there are 166 references remaining.
• After manual deduplication there are 158 references left.
• The final result is 158 references.
• A high number of references will be excluded by employing the inclusion and exclusion criteria when screening the title and abstract, and by reading the full text of articles/publications.
• The final list of studies are those included in your review.

Document your search

Documentation of the search makes your research reproducible and indicates that your methodology is sound. You will want to describe the search strategy that led to the included studies.

• names of databases
• name of vendor/host of databases (did you use Medline through PubMed or Ovid? Embase on Ovid or Embase.com?)
• last date of the search or alert service
• the search terms used. Include both subject headings and text words
• how the search terms were combined
• the limitations where they were used: publication dates, study designs, languages, etc.
• whether reference lists were reviewed
• number of retrieved records
• number of internal duplicates/number of duplicates removed
• number of articles after removal of duplicates

Check the journals’ instructions for authors to ascertain any specific requirements on how to report the search strategy. It may also be a good idea to look at published reviews in your preferred journal to see what is customary. For instance, some journals encourage authors to give details of the full search strategy in an appendix.

Documentation of the search strategies can be done by:

• Describing the search strategy in plain text in a separate section of your text, where you inform your readers how you made your choices and proceeded.
• Documenting precisely how your literature search was performed, by saving or copying the search strategy from each database. These can be organised in an appendix and can be presented in a way similar to the examples above.
• A flow chart can illustrate the workflow from the initial search results to the finally included studies. The PRISMA flow chart is a well-known chart for documenting the search process. The PRISMA ( Preferred Reporting Items for Systematic Reviews and Meta-Analyses ) guidelines are a set of minimum criteria for reporting systematic reviews and meta-analyses. It includes a chapter on reporting the literature search.

Example of how documentation of search strategies can be done in a section of a text

Studies included in this review were located from searching PubMed, Embase Ovid and Web of Science (last search [date]). The literature search included MeSH-terms and text words in the following combination: electronic cigarettes OR tobacco vaporizers AND tobacco exposure AND obstructive lung diseases. The full search strategy in PubMed included the following MeSH-terms and text words: (electronic cigarettes[MeSH Terms] OR electronic cigaret* OR e-cigaret* OR electronic nicotine) OR ((Nebulizers and Vaporizers[MeSH Terms] OR vapor* OR vapour* OR vaper* OR vaping OR vaporizer*) AND (Tobacco products[MeSH Terms] OR Smoking[MeSH Terms] OR Tobacco Use Cessation Products[MeSH Terms] OR Tobacco use[MeSH Terms] OR Smoking cessation[MeSH Terms] OR Nicotine[MeSH Terms] OR smoking OR nicotine ))) AND (Inhalation Exposure[MeSH Term] OR Tobacco Smoke Pollution[MeSH Term] OR passive OR exposure OR pollution OR second hand) AND (Asthma[MeSH Terms] OR Bronchitis[MeSH Terms] OR Pulmonary Disease, Chronic Obstructive[MeSH Terms] OR Asthma OR Bronchitis OR Chronic Obstructive Pulmonary Disease* OR COPD OR Obstructive pulmonary disease* OR Chronic Obstructive airway Disease* OR Obstructive airway disease* ).

The search was adapted to Embase with the following Emtree terms: electronic cigarette, vaporization, smoking, exposure, obstructive airway disease, asthma, bronchitis and chronic obstructive lung disease, and to Web of Science by searching by topic. There were no restrictions on language or publication dates. The reference lists of the included articles were screened for additional references.

For further input and advice on systematic searching, consult your library, help pages in databases and literature on the topic. Some libraries offer courses in systematic searching, or they will perform such searches for you on request.

Gusenbauer, M.,& Haddaway, N.R. (2021). What every researcher should know about searching - clarified concepts, search advice, and an agenda to improve finding in academia.  Research Synthesis Methods 12 (2), 136-147.  https://doi.org/10.1002/jrsm.1457

Haraldstad, A. M., & Christophersen, E. (2015). Literature searches and reference management. In P. Laake, H. B. Benestad, & B. R. Olsen (Eds.),  Research in medical and biological sciences from planning and preparation to grant application and publication  (pp. 125–166). Amsterdam: Elsevier.

Higgins, J., & Thomas, J. (Eds.). (2020). Cochrane Handbook for Systematic Reviews of Interventions, Version 6.1. https://training.cochrane.org/handbook/current.

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