Compare the registered or reported sample size and population against your protocol criteria, then record include, exclude, or query with the exact field values you compared. A mismatch in size or population is a discrepancy to resolve against the protocol, not an automatic exclusion.
Run the comparison in order
- Pull the sample fields from the study record and from the report: registered enrollment, reported analyzed sample, and the population description (age range, condition, setting). Note each value and where it came from.
- Place those values beside the matching protocol criteria for sample size and population. Mark each criterion as met, unmet, or unclear, and write the specific numbers or descriptors on both sides.
- Decide the outcome. Exclude when the population clearly falls outside a protocol criterion. Query when the record and report disagree, when a field is missing, or when the reported analyzed sample differs from the registered enrollment without explanation. Include only when the values satisfy the criteria.
- Record the rationale with the field values compared, the decision, and the date. This entry supports the exclusion reasons and selection counts that PRISMA 2020 asks reviews to report.
Why size and population mismatches happen
A registered enrollment target and a reported analyzed sample describe different things: one is planned recruitment, the other is who was actually analyzed. ClinicalTrials.gov registration and results fields separate study design, eligibility, and reported results, so read each field on its own terms. A gap between them is a question to resolve with the authors or the full text before you assign a decision.
Keep the audit trail
Cochrane Handbook guidance on selecting studies emphasizes documenting how records are managed and decisions made. Log the source of each value (registration record, abstract, or full text) so a later reviewer can repeat your comparison. When you query, state the exact discrepancy and the field values on each side; that record becomes your exclusion reason if the study is later dropped.