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Systematic Reviews

Information on how to conduct systematic reviews in the health sciences.


Evidence synthesis refers to any method of identifying, selecting, and combining results from multiple studies.The type of evidence synthesis, or literature review that you conduct depends on the type of project that you are doing.  Literature reviews fall along a spectrum in terms of being systematic, with systematic reviews requiring every aspect of the methodology to be systematic, and narrative reviews, which do not require every aspect to be systematic.  Despite which search methodology best matches your project's needs, you can still take a systematic approach to strengthen your review. 

The chart below is a useful guide to differences between methodologies at each end of the spectrum: a systematic review and a narrative review.

To learn more about the different types of literature reviews consult this article, A typology of reviews: an analysis of 14 review types and associated methodologies, which defines 14 types of reviews.  There is a helpful summary table on pp. 94-95.

If you're not sure what type of review is right for your quantitative review, use this tool to find the best  types of review:

Systematic Review versus Literature Review Searches

Systematic Review

  Literature Review

Search strategies must be replicable

  • Document database names & platforms (Medline/Ovid, CINAHL/ EBSCO), search dates, all search terms & limits used in the methods section of a publication or in an appendix.
  • Informationists who create the search strategy often write the methods section.

Search strategies do not need to be replicable

  • Normally not published in the methods section.
  • Are less detailed when published.

Follow specific search methodologies that ensure  comprehensive results

  • Search strategies are highly sensitive to find relevant articles.
  • Many databases are searched.
  • Other sources, such as & hand searching, are used.

Searches vary in how comprehensive they are

  • Search strategies may not be as comprehensive in:
    • search terms used
    • the number of resources that searched.

Require a significant time commitment

  • Because of the methodology of systematic reviews, they can take 18-24 months to complete, even with a team involved.

Take much less time

  • The time frame depends on the topic, what you are trying to achieve with the search, & thus how comprehensive the search needs to be, but it can be significantly shorter.

Typically retrieve high number of results

  • Searches produce large numbers of search results because of the sensitivity of an SR search strategy.
  • Citations are excluded after manual review.

Retrieve lower number of results

  • These searches retrieve fewer results than SR search strategies because they are more specific than sensitive.
  • A manual review may not be necessary.

Require a team

  • Generally, two or more individuals independently review each article separately to determine whether it meets inclusion criteria.
  • Conflicts are solved by a third party. 

Can be completed by individuals

  • Results do not need to be reviewed for inclusion or exclusion by multiple individuals.


  • Answers a specific clinical question.
  • Has specific inclusion & exclusion criteria.
  • Uses methods for assessing bias.

Does not use a protocol


Adapted from Penn State Hershey