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Systematic Reviews

What is Citation Searching

“Citation searching uses the citation network surrounding a source study to identify similar studies. A citation network consists of the studies that are cited by a source study (ie, the reference list) and the studies that cite a source study. Citation searching in the context of a systematic review usually starts with one or more studies that meet, or that have similar content to, the inclusion criteria.”1

Citation searching uses seed references (usually the set of included records from the results of a database search) and checks whether additional relevant articles can be found through forward citation searching and backward citation searching.

You may like to refer to the Guidance on terminology, application, and reporting of citation searching: the TARCiS statement. It provides guidance for systematic reviewers on when and how to conduct citation searching and on how to report it.

Forward Citation Searching

Forward citation searching looks forward in the literature. It takes relevant articles (seed articles) and looks for newer articles that have cited them. It is also known as forward snowballing or cited by searching.

Useful databases for forward snowballing are:
Backward Citation Searching

Backward citation searching looks backwards in the literature. It takes relevant articles and looks at their reference lists for other articles that might be relevant. This technique is also called backward snowballing or reference searching.

Useful databases for reference searching are:

If reference lists are reviewed manually it is called reference list checking.

It can be fruitful to search the reference lists of relevant existing systematic reviews and meta-analyses, identified studies (included and excluded studies) or other related articles.

According to Cochrane, searching reference lists is mandatory; reference lists in included studies and any identified relevant systematic reviews should be checked (Cochrane Handbook, 4.3.5.)

Web of Science Citation Reports

  1. Gather a list of PMID numbers for each seed article.
  2. Launch Web of Science
  3. Enter each PMID number into the search bar separated by OR. Select PubMed ID from the list of available search fields. Click search. Any articles that don't appear in Web of Science will need to be analyzed via another source, such as PubMed or Google Scholar. 
  4. Click on Citation Report.
  5. Export full report as text or Excel file.
  1. Gather a list of PMID numbers for each seed article.
  2. Launch Web of Science
  3. Enter each PMID number into the search bar separated by OR. Select PubMed ID from the list of available search fields. Click search. Any articles that don't appear in Web of Science will need to be analyzed via another source, such as PubMed or Google Scholar.
  4. For each citation, click on the number above References to see the cited references. 
     
  5. Select all citations and click "Add to Marked List". Not all articles will be available in Web of Science. Make note of those citations in case you need to seek the article elsewhere.
  6. Repeat steps 4 and 5 for each seed article. Web of Science will automatically delete duplicates from your marked list. Once you have added all references to the marked list, navigate to the list by clicking on the folder icon on the Web of Science homepage.
  7. Select all references and export them in a format of your choosing.

Reference and Recommended Reading

1.   Briscoe S, Bethel A, Rogers M. Conduct and reporting of citation searching in Cochrane systematic reviews: A cross-sectional study. Research synthesis methods. 2020;11(2):169-180.

2.  Haddaway, N. R., Grainger, M. J., & Gray, C. T. (2022). Citationchaser: A tool for transparent and efficient forward and backward citation chasing in systematic searching. Research synthesis methods, 13(4), 533–545. 

3.  Hirt J., Nordhausen T., Fuerst T., Ewald H., TARCis study group, Appenzeller-Herzog C. (2023). The TARCiS statement: Guidance on terminology, application, and reporting of citation searching.  medRxiv.  https://doi.org/10.1101/2023.10.25.23297543