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Systematic Reviews and Evidence Syntheses: Searching for primary studies

How to do a systematic review. How to find systematic reviews.

General tips on literature searching

Methodological search filters

Methodological search filters (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 verify that you're using the most appropriate filters for your topic.

Searching for primary studies

So far you've searched for systematic reviews. The next part of searching for studies 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 two broad stages:

  • 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 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.

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

  • Cochrane Central Register of Controlled Trials via The Cochrane Library
  • Embase
  • Medline/PubMed
  • PsycINFO
  • Web of Science

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

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 1 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

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