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Systematic Reviews: A How-To Guide

Step 3: Search for Studies

When you're ready to start searching the literature expect to:

  • Consult with a librarian!
  • Search multiple databases
  • Manually search reference lists of relevant studies
  • Decide on a plan for handling grey literature (unpublished, or research not located in traditional databases)
  • Document the search strategies used
  • Manage citations - Sladen provides EndNote for citation management

Work with a Sladen Librarian

The Sladen Librarians are available to work with you on your search, conducting the search, providing guidance on search strategy development and database recommendations, documenting the search strategies used, and writing the search methodology portion of the review. 

Let's get started:

Begin by answering a few questions about your project so we can approach your search correctly: Systematic Review Questionnaire

Based on how you answered the questions, at the end of the questionnaire, you will be provided a link to a form to request help from a librarian. This is a second step that must be completed in order for the library to receive your request.  

Please call 313-916-2550 or email: us with any questions 

Finding Studies for Systematic Reviews

"Systematic reviews require a thorough, objective and reproducible search of a range of sources to identify as many eligible studies as possible (within resource limits). This is a major factor distinguishing systematic reviews from traditional narrative reviews, which helps to minimize bias and achieve more reliable estimates of effects and uncertainties. A search of MEDLINE alone is not considered adequate. Research evidence indicates that not all known published randomized trials are available in MEDLINE and that even if relevant records are in MEDLINE, it can be difficult to retrieve them" (Cochrane Handbook for Systematic Reviews of Interventions, section 4.2.2)

In order to be comprehensive, more than one resource or type of resource, including non-journal literature, should be searched. Studies can be found using a combination of sources:

  • Bibliographic databases: Choose the appropriate databases for your topic. A librarian can help point you in the right direction. For typical health care studies good databases to start at include:

The Cochrane Central Register of Controlled Trials (CENTRAL)

  • Checking the reference lists of relevant studies
  • Hand searching key journals and conference abstracts on your subject
  • Contacting key authors, experts, or manufacturers related to your subject for possible unpublished studies or unreported outcomes 
  • Search appropriate Internet resources. This can be a good way to locate grey literature. "Grey literature" is comprised of informally published and unpublished materials, such as technical reports, statistical reports, theses, and clinical trial registries. Grey literature can be difficult to locate.
  • A note about using Google Scholar: Google Scholar should not be considered a major source of literature for a systematic review. Because the search algorithm of Google is unknown, searches performed within this database cannot be reliably reproduced. 

Suggested databases

Search Tips

  • Beware of language, date, and publication bias. See Cochrane Handbook 4.4.5 for more info.
  • Search using a combination of index terms (subject headings) and keywords
  • Identify synonyms for your key concepts and include those in search
  • Not all databases use the same index terms. You will need to modify your search terms for each database used.  
  • When searching with keywords, pay attention to possible British/American spelling differences and word variations; such as in "color" vs "colour". Most databases do not auto-search word variations in a keyword search.

Documenting the Search

A Sladen Librarian can assist with this step. Documentation is provided to you when a Librarian performs your searches. 


Reproducibility and transparency are important traits of high-quality systematic reviews. It is important to keep clear documentation of your literature searching activities. This involves:

  • Keep a line-by-line description (preferably a copy & paste) of each search strategy used, number of results retrieved, and in which database
  • Document database name and date each search was carried out

If your review process spans many months, searches may need to be re-run in order to capture the most recent results.

The PRISMA 2020 Checklist (Items #6-7) provides detailed information on the elements to document when carrying out a systematic review search.

EndNote for Citation Management

Systematic review searches can generate a ton of articles to work through and manage. The Sladen Library provides the reference management software EndNote for free to Henry Ford Health physicians, team members, and affiliated students.