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Systematic Reviews & Meta-Analysis

Learn about the systematic review and meta-analysis process

What is a Systematic Search?

The goal of systematic review searches is to identify all relevant studies on a topic. Therefore, systematic review searches are typically quite extensive. The process should be transparent and repeatable, meaning that others can use your process to repeat it for themselves.

Developing your search strategy is the key to ensuring that you find the right kind of evidence for your systematic review. Your search strategy refers to the specific keywords, subject headings, filters and connectors you will use to find relevant literature. The search terms for each one of your concepts should consist of keywords and subject headings when available.

Having already formed an answerable question before beginning your search, you now have the key topics and components necessary to build your search strategy. To help build your search strategy, it would be helpful to conduct a preliminary search and a final comprehensive search.

Preliminary Searches (non-systematic)

Conducting some preliminary, non-systematic searches on your topic will help you to:

  • Identify keywords and synonyms to use in your search
  • Find existing systematic reviews on any component of your topic and review search strategies included in the methods or appendix
  • Locate relevant articles that will likely be included in your study

Final Comprehensive Search (systematic)

When you have completed your preliminary searches, consider the following when conducting the final search:

  • Make sure all keywords for each concept as well as synonyms/related terms have been identified
  • Identify any databases and resources to search through the library's website or by discussing with a librarian
  • Once you are happy with your final search strategy, translate this search strategy to other database(s)
  • Run your search on more than one database
  • Choose a day to run all of your searches. This helps to reduce bias
  • Compile ALL results from all databases searched; export these results into a citation management tool and remove duplicates
  • Check the reference lists of all included studies; also check whether the included study has been cited using Scopus, Web of Science, or Google Scholar
  • Determine relevant grey literature sources and search with modified strategies

Identifying Search Terms

Keywords are words or phrases that can be searched for in different database fields such as title, abstract, author keywords, journal etc. You can use the PICO, SPICE, SPIDER, etc. concepts of your research question as your preliminary key terms. It is important to consider the synonyms for each concept so that you have as few gaps as possible in your extensive search.

Below is an example of how you may keep track of your keywords:

  Key Terms Synonym A Synonym B


Subject Headings are assigned to articles, ebooks, and any other resources found in a database by indexers in order to identify the main topics of an article. Different databases use their own subject heading classification systems.

Some examples of subject heading systems or controlled vocabulary include Medical Subject Headings (MeSH) and Library of Congress Subject Headings (LCSH). It useful to use subject heading, since they are used to tag resources on similar subjects. When you search using a subject heading, you will get more relevant results in return.

Not all databases will have subject heading searching and for those that do, the subject heading categories may differ between databases. This is because databases classify articles using different criteria.

It is also helpful to keep track of your subject headings in a similar fashion as you would with your keywords:

  Key Terms Synonym A Synonym B Subject Headings

Search Hedges are search strings created by experts to help you retrieve specific types of studies or topics; a hedge will filter your results by adding specific search terms, or specific combinations of search terms, to your search.

Hedges can be good starting points but you may need to modify the search string to fit your research. Resources for hedges:

Finding Evidence Through the Library's Resources

Once you have identified all of your keywords and subjects, you will be ready to develop your search strategy. You can find more information on developing a search strategy and searching for evidence through the library in the following guide: