4.2.6.2 Citation searching

Citation searching is an umbrella term for finding further relevant references to studies by authors who are deemed experts on the review question. Backward citation searching is the process of reviewing the reference lists of studies that meet the inclusion criteria (seed references). Forward citation searching is a search to see what references have cited the seed references. The TARCiS Statement provides ten recommendations, with rationale and explanation, on when and how to conduct and report citation searching, based on a four-round Delphi study (Hirt et al. 2024). For review questions that are complex and difficult to search for, backwards and forwards citation searching should be seriously considered as a supplementary search.

Google Scholar (free) plus Web of Science and Scopus (via subscription) are citation index sources for citation searching. It is advisable to search two of these for extensive coverage. This is because seed references may be found in one source and not another (Hirt et al. 2024). citationchaser and SpiderCite  are free tools for conducting backwards and forwards citation searching.

Forwards citation searching using Google Scholar can be undertaken using the ‘Publish or Perish’ software.

Deduplicating the results from records already screened is important. For an online tutorial ‘Retrieving supplementary citation searching results from several citation indexes’ using citationchaser, Web of Science and Scopus, see https://osf.io/jaeu5 .

The number of records added to the search is added to the top right of the PRISMA flowchart. If any tools are used to perform citation searching, these should be indicated.