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Doing the literature review: Reporting your search strategy

Reporting your search strategy

PRISMA, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses, is a minimum set of items for reporting in systematic reviews and meta-analysis. Even when your goal isn't a systematic review or a meta-analysis, this set of items can also help you to search in more systematic way and to make your search more transparent.

The PRISMA Statement consists of a checklist and a flow diagram.

The checklist consists of 27 items. It guides you through the choices you have to make when you do a literature review. For example: what are criteria for eligibility (when do you include a paper or not), which databases have you used, what was the search strategy? This will make your literature review more systematic, better structured, and it will be easier to write down the steps in your paper or article. 

The flow diagram shows the ‘flow’ of information in the different phases of a systematic review, by showing the number of records identified, included and excluded, and the reasons for exclusions. In the academic literature you will find a lot of variants of the flow diagram.

In 2021, the PRISMA extension for searching was published: a checklist of 16 items to report literature searches in systematic reviews. They are more specific than the PRISMA Statement. 

Examples of the PRISMA flow diagram

In the PRISMA flow diagram you summarize the study selection process. In the diagram you report:

Identification

  • The number of records found by searching databases. You can add the number of records found in each database used.
  • The number of records found via other ways, for example via the reference lists, via citing articles, or via experts.

Screening

  • The number of unique records found after removing duplicates - the articles found in multiple databases.
  • The number of records screened – this means in this stage reading the titles and abstracts.
  • The number of records excluded, because they do not meet your inclusion criteria (for example, the age group of the participants in the study doesn’t match) or fit your exclusion criteria (for example the article is in French).

Eligibility

  • The number of full text articles assessed for eligibility – here you also use the inclusion and exclusion criteria. You might also lose some articles because you don’t have access to the full text.

Included

  • The number of studies included in the review. The last box (the number of studies included in quantitative synthesis) is only applicable when you are doing a meta-analysis. 

This is the visualization of these steps in the flow diagram as described in the PRISMA statement:

Source: Moher D, Liberati A, Tetzlaff J, Altman DG, The PRISMA Group (2009). Preferred Reporting Items for Systematic Reviews and MetaAnalyses: The PRISMA Statement. PLoS Med 6(7): e1000097. doi:10.1371/journal.pmed1000097

In the other tabs you can see examples of how the PRISMA flow diagram is applied in academic articles. 

Flow diagram in Gerontologist - Bom e.a.

Source: Bom, J., Bakx, P., Schut, F., & van Doorslaer, E. (2018). The impact of informal caregiving for older adults on the health of various types of caregivers: A systematic review. The Gerontologist, 59(5), e629-e642. doi:10.1093/geront/gny137

Source: Igalla, M., Edelenbos, J., & van Meerkerk, I. (2019). Citizens in action, what do they accomplish? A systematic literature review of citizen initiatives, their main characteristics, outcomes, and factors. VOLUNTAS: International Journal of Voluntary and Nonprofit Organizations, 30(5), 1176-1194. doi:10.1007/s11266-019-00129-0

Flow diagram Addiction

Source: Jones, A., Remmerswaal, D, Verveer, I, Robinson, E., Franken, I.H.A, Wen, C.K.F., & Field, M. (2019). Compliance with ecological momentary assessment protocols in substance users: a meta-analysis. Addiction, 114(4), 609-619. doi:10.1111/add.14503

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