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Systematic Review Program: Lit Search

Planning the search

Use the hyperlinks in this mindmap to navigate to other sections of the LibGuide.
Adapted from IOM Standards 2.1.3, 2.5.1, 3.1, 3.2, 3.4.1, 5.1.6

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Reduce bias with a comprehensive literature search

It is important to locate and identify all relevant studies using a wide range of resources and search methods for the systematic review. This will help to minimize bias and produce reliable estimates and results.

This is achieved by developing and using a systematic, comprehensive, transparent,  and reproducable literature search. 

For more information see: 

Finding What Works in Health Care: Standards for Systematic Reviews (full report). Institute of Medicine of the National Academies, The National Academy Press. 


Higgins JPT, Green S (editors). Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 (updated March 2011). The Cochrane Collaboration, 2011. Available from


The Cochrane Methods Bias (CMB) strives to raise awareness of the problem of bias and is exploring important questions with respect to the epidemiology of research results and outcomes".

Core biomedical databases

Cochrane Collaboration's rationale for using multiple databases can be found here: Minimizing bias 

For all Cochrane Collaboration systematic reviews the following databases are required to be searched. 6.2.1 Bibliographic databases.

IOM's Key Information Sources [ Box 3.2 ] includes the databases listed above  along with one more:

For more details:


Literature searches in bibliographic databases for systematic reviews may produce thousands of records.

Your ability to successfully organize and manage these records will impact your ability to complete your systematic review.

Librarians typically do not participate in the creation of databases used to manage results, but we can provide you with resources about managing search results. See: Data Management 

How many studies retrieved will be included in the systematic review?

Sampson [et al.] found the average percent of studies retrieved making it into a final systematic review is around 3%, with a range of 3-6 articles meeting inclusion criteria per 100 articles examined. 

"This information is useful in several ways: 

  • Once the search has been completed, the reviewers can make some preliminary estimates of the number of studies that will need to have data extraction and synthesis, the intellectual work of the review.
  • Once screening is completed and the number of included studies is known, the information specialist can determine if precision is unusually high or low. Unusually high precision may indicate that the search was not sufficiently broad to identify all relevant studies."

Sampson M, Tetzlaff J, Urquhart C. Precision of healthcare systematic review searches in a cross-sectional sample. Res Synth Methods. 2011 Jun;2(2):119-25. Epub 2011 Sep 27.

Grey literature

Grey Literature can be in either print or electronic formats and  is produced on all levels of government, academics, business and industry, but is not controlled by commercial publishers. (What is Grey Literature? New York Academy of Medicine, 2003.)

For many systematic reviews, most grey literature is found through searches of clinical trial registries and conference abstracts. 

HSLS Librarians are experts on Grey Literature. See HSLS Support for help with selecting Grey Literature resources.

Request systematic review help

To request a systematic review consultation:

What consultation services can be provided? see HSLS Support

Who's eligible?

  • faculty, staff and students in the Schools of the Health Sciences, University of Pittsburgh
  • UPMC Residents and Fellows
  • UPMC physicians with University of Pittsburgh faculty appointments

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