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Systematic Reviews

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

Validated Search Filters

Depending on your topic, you may be able to save time in constructing your search by using specific search filters (also called "hedges") developed & validated by researchers in the Health Information Research Unit (HiRU) of McMaster University, under contract from the National Library of Medicine.  These filters can be found on

Why Create a Sensitive Search?

In many literature reviews, you try to balance the sensitivity of the search (how many potentially relevant articles you find) & specificity (how many definitely relevant articles you find), realizing that you will miss some.  In a systematic review, you want a very sensitive search:  you are trying to find any potentially relevant article.  A systematic review search will:

  • contain many synonyms & variants of search terms
  • use care in adding search filters
  • search multiple resources, databases & grey literature, such as reports & clinical trials

Developing an Answerable Question

PICO is a good framework to help clarify your systematic review question.

P -  Patient, Population or Problem: What are the important characteristics of the patients &/or problem?

I -  Intervention:  What you plan to do for the patient or problem?

C - Comparison: What, if anything, is the alternative to the intervention?

O - Outcome:  What is the outcome that you would like to measure?


Beyond PICO: the SPIDER tool for qualitative evidence synthesis.

5-SPICE: the application of an original framework for community health worker program design, quality improvement and research agenda setting.

Creating a Search Strategy

A well constructed search strategy is the core of your systematic review and will be reported on in the methods section of your paper. The search strategy retrieves the majority of the studies you will assess for eligibility & inclusion. The quality of the search strategy also affects what items may have been missed. Informationists can be partners in this process.

Identifying Synonyms & Related Terms

For a systematic review, it is important to broaden your search to maximize the retrieval of relevant results.

Use keywords:  How other people might describe a topic?

Identify the appropriate index terms (subject headings) for your topic.

  • Index terms differ by database (MeSH, or Medical Subject Headings, Emtree terms, Subject headings) are assigned by experts based on the article's content.
  • Check the indexing of sentinel articles (3-6 articles that are fundamental to your topic).  Sentinel articles can also be used to  test your search results.

Include spelling variations (e.g., behavior, behaviour). 

Keywords vs. Index Terms

Both types of  search terms are useful & both should be used in your search.

Keywords help to broaden your results.  They will be searched for at least in journal titles, author names, article titles, & article abstracts.  They can also be tagged to search all text.

Index/subject terms help to focus your search appropriately, looking for items that have had a specific term applied by an indexer.

Combining Search Terms Using Boolean Operators

Boolean operators let you combine search terms in specific ways to broaden or narrow your results.

A SR Search Strategy

An example of a search string for one concept in a systematic review.

In this example from a PubMed search, [mh] = MeSH & [tiab] = Title/Abstract, a more focused version of a keyword search.

Search Limits

A typical database search limit allows you to narrow results so that you retrieve articles that are most relevant to your research question. Limit types vary by database & include:

  • Article/publication type
  • Publication dates
  • Species
  • Language
  • Sex
  • Subject
  • Ages

In a systematic review search, you should use care when applying limits, as you may lose articles inadvertently.  For more information, see, particularly regarding language & format limits.   Cochrane 2008 6.4.9