How do I check eligibility when a study's sample size differs between abstract and full text?

Use the full-text methods and results to establish the analyzed sample, then record the abstract or registry discrepancy in your screening log and decide inclusion on the full-text figure.

A sample size can differ between an abstract, a full text, and a registry entry because each reports a different stage of the study. The abstract may describe enrollment, the methods may describe participants analyzed, and a registry entry may describe the planned or target sample. Treat these as separate figures until the full text shows how they connect.

1. Read the full-text methods and results first and identify the number of participants actually analyzed for the outcome your review needs. Record the figure and the page or section where it appears. Expected result: a full-text sample figure tied to a specific analysis.
2. Compare that figure with the abstract and any registry entry, noting whether each number refers to planned enrollment, participants enrolled, or participants analyzed. Expected result: a short note explaining what each figure represents.
3. Record the discrepancy in your screening log, including the source of each figure and the full-text value you will use. Expected result: a traceable record that supports your inclusion decision and can be reported in your review's flow of studies.

PRISMA 2020 calls for transparent reporting of what studies were found and included, so a documented discrepancy helps explain your counts. ClinicalTrials.gov registration fields separate study design, eligibility, and reported results, which helps you see whether a registry number describes a planned target or a reported result. The Cochrane Handbook's guidance on selecting studies and managing records supports keeping this comparison in your screening documentation.

When the full text leaves the analyzed sample unresolved, mark the study as pending and check supplementary files, tables, or the registry results section before deciding. If the full-text figure still cannot be established, note the unresolved status and the specific figure you need.