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Systematic Reviews

Where and How to Search

Searching Strategy

The goal of systematic review searches is to identify all relevant studies on a topic. Therefore, systematic review searches are typically quite extensive. It is necessary, however, to strike a balance between striving for comprehensiveness and maintaining relevance when developing a search strategy. Increasing the comprehensiveness (or sensitivity) of a search will reduce its precision and will retrieve more non-relevant articles.

The goal of a systematic review search is to maximize recall and precision while keeping results manageable. Recall (sensitivity) is defined as the number of relevant reports identified divided by the total number of relevant reports in existence. Precision (specificity) is defined as the number of relevant reports identified divided by the total number of reports identified.  

Issues to consider when creating a systematic review search:   

  • All concepts are included in the strategy
  • All appropriate subject headings are used
  • Appropriate use of explosion
  • Appropriate use of subheadings and floating subheadings
  • Use of natural language (text words) in addition to controlled vocabulary terms
  • Use of appropriate synonyms, acronyms, etc.
  • Truncation and spelling variation as appropriate
  • Appropriate use of limits such as language, years, etc.
  • Field searching, publication type, author, etc.
  • Boolean operators used appropriately
  • Line errors: when searches are combined using line numbers, be sure the numbers refer to the searches intended
  • Check indexing of relevant articles
  • Search strategy adapted as needed for multiple databases

Adapted from Duke Systematic Review Guide:

Choosing Databases

First choose databases that make sense for your research question. Once you have databases chosen, use a search strategy that will find all literature on your topic. Use the spreadsheet below to keep up with your plans.

Subject Headings

Subject headings are a set of terms naming descriptors in a hierarchical structure that enables you to search at various levels of specificity. MeSH (Medical Subject Headings) is the (U.S.) National Library of Medicine's controlled vocabulary thesaurus and is used for indexing articles for MEDLINE. There are also various subject headings in most databases. Be sure to account for them in your search strategy.

Specification in Searching

There are many searches already created that you can use. These are called filters (or hedges) as they can be added to your topic or combined to limit to a particular population, intervention, study type, etc.

Grey Literature

Grey literature refers to materials and research produced by organizations outside of the traditional commercial or academic publishing and distribution channels. A systematic review can be biased when it fails to report crucial information that may be hidden in some grey literature. A search of grey literature is one way to address potentially biased reporting of research results in published material. Some examples of grey literature are theses, clinical trials, reports, fact sheets, government documents, and research transmitted through informal communication methods, e.g., blogs and podcasts. Grey literature can be the best source of up-to-date research on some topics; however, grey literature is usually not subject to peer review and must be evaluated accordingly.

Where to Search

Finding Research Outside of Databases

Outside of databases, there are other places you should look in order to find research.

In addition to looking into various other online sources, make a plan determining if you need to and how you will search reference lists. You may also want to search out authors by name and "hand search" relevant journals' tables of contents.

Searching Documentation

Document at least the following details of your search:

  • Databases searched
  • Search strings used and dates
  • Number of articles retrieved and internal and external duplicates

Keep the following:

  • Searches saved in your database accounts
  • Citations in one place (e.g., Endnote, RefWorks, or Excel)
  •  a spreadsheet organized by article and sub-organized by preliminary inclusion and exclusion criteria to track why you included and excluded articles for more in-depth review
  •  detailed notes of in-depth reviews for each article organized by specific criteria