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Systematic Reviews and Evidence Syntheses: Searching for studies

How to do and find systematic reviews.

Searching for systematic reviews

Once you have defined your question you can start the searching process. The first step in searching for studies is to locate previously conducted systematic reviews in your area of interest. This has three main purposes:

  1. To verify that your question hasn't already been answered
  2. To verify that there are no other review protocols registered with researchers already looking at the same question
  3. To identify related systematic reviews that will need to be accessed so that you can review the reference lists for relevant primary studies.


Useful databases for identifying systematic reviews

Searching for primary studies

After searching for systematic reviews, the next stage is to find other 'primary studies' e.g. trials, diagnostic accuracy studies, qualitative studies. The identification of all studies relevant to your question is made up of three broad stages:

  • Initial scoping searches to inform the development of the protocol and set parameters of the search.
  • Development of a structured search strategy that is run across multiple databases
  • An iterative process for finding further studies through hand search of relevant publications, reviewing reference lists, citation searching, contact with authors and location of on-going studies.

The guides below provide an introduction to locating studies for different types of systematic reviews (therapeutic, diagnostic, qualitative...). You can also contact your outreach librarian or subject librarian for help and advice.

Databases to search for primary studies

The development of a structured search strategy that is run across multiple databases is a key stage in identifying primary studies for inclusion in a systematic review. These are some of the databases relevant to systematic reviews in health care. Additional or alternative databases should be searched depending on your question.

Consult your outreach or subject librarian for advice on relevant databases for your question.

These databases and more can be accessed via Databases A-Z.

Reporting your search

You will need to document your search in order to comply with the Preferred Reporting Items for Systematic reviews and Meta-analyses (PRISMA).

This is what you need to record:

  • Databases searched – including version and dates of coverage
  • Summary of search terms used, plus full electronic strategy for at least one database
  • Any limits applied e.g. language, date, study type
  • Other search methods applied e.g. screening reference lists, forward citation searching, web searching and contact with authors

General tips on literature searching

Methodological search filters

Methodological search filters (or "hedges") are often applied to searches to retrieve study types that are relevant to answering the question posed in the systematic review. 

For example, for systematic reviews of therapeutic interventions it's customary to restrict the search to randomised controlled trials.  The guides below have information on methodological search filters.

Please contact your outreach or subject librarian to check that you're using the most appropriate filters for your topic.