Skip to main content

Systematic Review: 2. Test and run search

Check your search strategy

It is important to carefully check your search strategy for errors and to test it to determine the effectiveness of the search terms you have chosen.

A number of factors influence the recall or precision of a search strategy, including the correct use of boolean operators and the use of relevant subject headings.  You can improve the quality of your search strategy by referring to an appraisal checklist such as:

 

     Search appraisal 10 point checklist 

     An Evidence-based practice guideline for the peer review of electronic search strategies 

Test your search strategy

Once you have discovered subject headings and words/phrases that seem appropriate for your Systematic Review topic it will be necessary to do some testing to determine if all the terms you have found will return useful results.

There are several steps to start testing your subject headings and words/phrases:

  • Explore the subject heading  trees if they exist in your chosen database to determine if you need to 'explode'  any subject headings
  • Check for any subject headings descriptors (or scope note ) to find additional synonyms or alternative terms that could be incorporated into your search.
  • Identify any terms that are retrieving large numbers of irrelevant papers.

When you are satisfied with your search terms, test your completed strategy in a key database:

  • Does it retrieve any papers from your gold set  that are contained in that database?
  • Are the results of the search relevant to your topic?  What proportion are irrelevant?

    Smart searching tool 

Select filters of limits

Based on your inclusion  or exclusion  criteria, identify any appropriate limits, and test their effect on your search.

Commonly applied limits  for systematic reviews include English language and human (not animal) limits, however, if other limits such as time limits are used, they must be documented and defensible.

It is also possible to use specific search filters  that have been designed and tested to retrieve particular types of studies, such as randomised trials.

 


   ISSG Search Filter resource 

Select databases and other information sources

After testing, you can select a range of databases for your final searches.  One database is inadequate, and will find an unrepresentative set of studies, increasing the risk of bias.

Three main databases used for systematic reviews are Ovid Medline EMBASE  and Cochrane CENTRAL .

In addition to these sources, researchers often use CINAHL Plus  and PsycINFO . 

They can be supplemented by other more subject specific databases.  A list of databases can be found in:

 

     Databases by subject library guide 

     Subject-based library guides 

 

You are often required to search additional sources.  This may involve checking reference lists or citations of relevant studies, hand searching journals, contacting experts in the field, and searching grey literature  to identify unpublished material such as organisational reports and theses.  At this time it is a good idea to consult a Subject Librarian  for further advice.