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Systematic Reviews: Search for studies

A guide for researchers undertaking a systematic review

Searching for studies

Step 1 - Formulate your question and translate into your search strategy

Step 2 - Identify the key concepts. This Search strategy planner will help you map out your key concepts and formulate your search.

Step 3 - Develop search terms. The Compose a search guide will demonstrate how to compose a search and test it on a sample of library databases.

Keyword searching

Keyword searching involves using key terms and phrases to identify individual results that contain those terms in the main fields of their record in the database, such as title and abstract. 

As authors may use different terminology to describe the same concept, when keyword searching it is important to consider and include all relevant synonyms and alternate terms for your concept in order to ensure you are locating all relevant results on your topic.

Keyword searching is the most common form of searching, and you probably do it every day when you search Google!

When keyword searching you may wish to include database syntax to help you formulate your search for more complex queries. For example:

Type Definition Example
Truncation symbols Allow you to search the root of a word, with any ending. Austral* = Australia, Australian, Australasian
Wildcards Use within words to search for alternate spellings or word forms. colo#r = color or colour
wom#n = woman or women
Adjacency operators Find keywords within a certain number of words of each other. mental adj5 health = finds the words 'mental' and 'health' within 5 words of each other. For example, this would find articles with the phrase "mental and emotional health"
Post-qualifiers Search for keywords in only certain fields of the record. education.ti,ab = searching the title and abstract fields only for the word education

IMPORTANT: Always check the Help menu of the database you are using to check the syntax of that particular database.

This Database Syntax Cheat Sheet developed in-house will assist you to translate your search across databases.

The Polyglot search translator tool automatically translates database syntax from a Medline (Ovid) or PubMed search strategy to other resources. NB this does not translate subject headings.

Subject heading searching (MeSH, Emtree, SH)

For systematic searching it is important to search both keywords and Subject Headings where possible. This is to ensure you have conducted a comprehensive search and identified as many relevant articles as possible.

Key features of subject headings:

  • Subject headings come from a thesaurus of allowable terms and relate to the main concepts in each record in the database. Subject headings are therefore consistent across all records in a database on the same topic, regardless of the terminology and phrasing an author has used in their title and abstract. For example, articles referencing 'heart attacks' may all be classified under a 'Myocardial infarction' subject heading.
  • Each database uses its own thesaurus of subject headings, so searches containing subject headings will need to be modified for each database you are using. Not all databases use subject headings.
  • Use the Help menus in the databases to determine how to apply subject headings in your search.
  • Subject headings for each of your key concepts should be used, regardless of whether you already have used a keyword for that topic.
  • Subject headings do change over time, you may need to use multiple headings for the same topic

Keywords or Subject Headings

If you only use keywords in your search strategy, you could miss articles if not all relevant terms are included in your search.
If you use controlled vocabulary (subject headings) only, you could miss articles that have not been indexed yet or have older indexing.

For further information view Curtin University's "Keywords vs Subject Headings" video:

You might also be interested to read the following paper on this topic, co-authored by one of our UWA Librarians. 

Solomons, T., & Hinton, E. (2021). Federated searches: why a one-stop shop approach to literature searching falls short for evidence synthesis. JBI Evidence Synthesis, 19(6), 1259-1262. 

Text mining tools

Text mining tools can assist you to establish appropriate keywords and subject headings for your topic, visit the text mining and data mining guide for further information. The Systematic Review Accelerator (SRA) is free software developed at Bond University which can help translate a Medline/PubMed search strategy to other major databases.

Use Boolean to combine search terms

You can use the Boolean AND and OR to combine your keywords:

AND - use to combine keywords for different concepts e.g. diet AND exercise AND obesity
OR - use to combine keyword synonyms e.g. diet OR nutrition

Concept 1 Concept 2 Concept 3
(diet OR nutrition OR "healthy eating")        AND (exercise OR "physical activity" )       AND (obesity OR overweight)

Search filters

Validated search filters (sometimes called hedges) have been developed by expert searchers as a method of most effectively searching for a particular topic or set of results in a particular database.

Validated search filters take the work out of developing your own search strategy. Sources of search filters include:

Keeping current

Once you have conducted your initial searches, you will need to continue to monitor new studies being published. These may not be included in the systematic review once you have started the process of data analysis, but you should be aware of any developments.

For more information on setting up alerts, visit our Keeping your research current guide.

 

There are various search builder tools that can assist with the search process.

  • The Systematic Review Accelerator (SR-Accelerator is a suite of tools developed by the Bond University to speed up steps in the Systematic Review (SR) process. They have made it freely available for anyone to use. 
  • The Systematic Review Toolbox - a community-driven and searchable catalogue of tools that support the systematic review process across multiple domains. 

There are free browser plug-ins that may help you find the full text pdf from Open Access (OA) sources. Download the internet browser extensions from your app store.

  • LibKey: integrates with our UWA library subscriptions as well as other OA online sources
  • EndNote click: integrates with our UWA library subscriptions as well as other OA online sources.
  • Unpaywall: harvests open access online content from publishers and repositories

 

The databases and information sources you choose to search will depend on your research topic. 

Databases

You will need to ensure you search a wide range of subject specific databases in order to capture the full extent of published journal literature on your topic. Databases all index a different set of journals, and while you can expect some overlap you will also find unique content in each database. 

Most subject areas will have specific core databases that the majority of systematic reviews will use, and then subject-specific databases depending on the topic.  The library provides access to key databases such as;

If you're not sure where to start, you can:

Citations/References

Citations and references of key articles are an important supplementary source of published literature and will often help you to discover additional studies that have not appeared in the search results of your database searches.

Using resources such as Scopus, Web of Science and Google Scholar will make this a simple process. Search for a key article you already know of, and then use the database's functionality to link to citations and references for that article. 

For more information, visit our Citations, Altmetrics and Researcher Profiles guide.

The video below gives a short explanation of citation searching and how to do this in the Web of Science database.

 

Handsearching

Handsearching requires manual perusal of key journals or conference proceedings in order to identify any further studies of interest. Studies may be referred to not just in research articles, but also editorials, letters and news columns. Handsearching may not be required in all situations, but in certain circumstances, especially when looking at older material, it may be important.

Grey Literature

What is grey literature

Grey literature is literature that has not been formally published. This includes government reports, theses, clinical trial registries and conference proceedings. The grey literature can be an excellent source of unpublished or current studies and it is important to have considered it as part of your systematic review. 

Why is grey literature important?

Grey literature helps you to form a more complete view of all the evidence around a particular topic. It is important to include as part of your systematic review to minimise publication bias.

Searching for grey literature

  • Keep it simple! Focus on your key concepts, don't try to run long strings of search terms.
  • Choose key organisations, professional associations, government department websites and grey literature databases and directories.
  • Find similar systematic reviews on your topic, and how they have approached their grey literature search.
  • Record where, when and how you searched each resource.

Evaluating grey literature

Grey literature is usually not subject to peer review and should be evaluated accordingly. To assist with evaluation you may wish to refer to the AACODS checklist created by Jess Tyndall, Flinders University, covering:

  • Authority
  • Accuracy
  • Coverage
  • Objectivity
  • Date
  • Significance

Key sources of grey literature

Googling grey literature

To effectively search for grey literature using Google we recommend using Google Advanced Search.

Here you can enter your search terms and apply limits in the 'Narrow your results' section. For example:

Site or domain

Consider restricting to a site or domain, though you can only search one domain name at a time.

  • .edu or .ac for academic institutions
  • .org for organisations
  • .gov for government sites.

 File type

Much of the grey literature available on the internet is in the form of PDF documents. You can limit your results by file type:

  • Select 'Adobe Acrobat PDF' to limit to pdf results.
  • Or include filetype: followed by the required file extension in your Google search query. For example, if you're searching for PDF files about cancer diagnosis after COVID, your query would be “cancer diagnosis after covid filetype:pdf"

For more information about refining web searches see Google Search Help.  For more information about searching Google see our guide on Using Google and Google Scholar.

Repositories

  • Institutional repositories, including Australasian Open Access Repositories, provides access to digital theses and research papers
  • OAIster, provides access to worldwide digital theses, technical reports and research papers
  • OpenDOAR, a directory of academic open access repositories

Websites

  • Australian Institute of Health and Welfare, a comprehensive source for Australian health reports

  • BASE, a multidisciplinary search engine to scholarly internet resources created by the Bielefeld University Library in Germany. Finds articles, conference papers, reports etc

  • Campbell Collaboration Library, maintains and disseminates systematic reviews in education, disability, nutrition, social welfare, and crime and justice

  • CORE. a collection of open access research papers

  • CogPrints, an electronic archive for self-archive papers in psychology, neuroscience, linguistics, and many areas of computer science, philosophy and biology
  • Grey Matters, a practical tool and checklist for searching health-related grey literature
  • IDEAS on RePEc, an economics database providing access to working papers and other research
  • OpenGrey, (formerly SIGLE), covers science, technology, biomedical science, economics, social science and humanities grey literature
  • The Grey Literature Report, a bimonthly publication of The NY Academy of Medicine Library, highlighting new grey literature publications in health services research and selected public health topics
  • WHOLIS (World Health Organization library database) includes international material from a variety of sources
  • Mednar, a deep web search engine that conducts real-time searching of peer-reviewed medical resources
  • WorldWideScience, a global science gateway comprised of national and international scientific databases and portal.

Trial registries

Catalogues

  • Trove, a database of content and holdings from Australian libraries, museums, archives and research organisations. Includes reports, working papers, theses, conference proceedings, and unpublished material
  • WorldCat, the world's largest network of library content and holdings, including theses and dissertations 

For further information view Western University's "Grey Literature Tutorial":

Webinar : Developing a robust search strategy for systematic reviews

This webinar recording covers:

  • Types of reviews
  • Definition of systematic reviews
  • Checking for prior reviews/
  • Search strategy planning & where to search
  • Keywords & Subject Headings
  • Boolean Operators AND & OR, Truncation & Wildcard searching
  • Grey literature
  • Managing search results in EndNote & Covidence
  • PRISMA reporting standards
  • Meeting with a librarian for review support
     

Webinar : Systematic review searching Ovid Medline

This webinar recording provides a demonstration of developing a search strategy in the Ovid Medline database for health-related reviews. It covers how to:

  • Find seed references from which keywords and Mesh Subject Headings are harvested into a Search Planner Concept Table to then create a search strategy
  • Proximity search operator ADJ
  • Editing and saving search strategies online
  • Testing that the search strategy captures seed references
  • Reporting search strategy so it is transparent & reproducible
  • Tips for increasing/decreasing search results


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