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Systematic Reviews: Searching for studies

A guide for researchers undertaking a systematic review

Searching for studies


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.  

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


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.

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 The grey literature can be an excellent source of unpublished or current studies and it is important to have considered it as part of your systematic review. For more information, visit our Grey literature page.


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.

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 Guide for Systematic Reviewers developed by Flinders University Library is a very useful tool


Subject heading searching

In addition to keyword searching, systematic reviewers should be using subject heading searching where possible. This is to ensure full coverage of all possible study identification methods.

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


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:


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.

The easiest way to do this is to set up search and citation alerts in databases and other information resources where possible. To do this you will need to create personal accounts in each individual resource.

You can set up alerts for:

  • specific search strategies in databases;
  • citations to specific publications or authors;
  • new publications by specific authors;
  • new publications in specific journals;
  • general Google and Google Scholar searches.

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

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.

Kopernio: integrates with our UWA library subscriptions as well as other OA online sources.

Unpaywall: harvests open access online content from publishers and repositories.


Putting it all together

Composing a search

For more information on structuring your search, check out our Compose a search guide.

Image source: Pixabay, licensed under a CC0 Public Domain license.

Citation searching

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

Text mining tools

Text mining tools can assist you to establish appropriate keywords and subject headings for your topic.

Some tools include: