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
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:
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When you are satisfied with your search terms, test your completed strategy in a key database:
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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.
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
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relevant studies, hand searching journals, contacting experts in the field, and searching grey literature to identify unpublished material such as organisational reports and theses.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.
