A Revised Classification Framework for Studies in Systematic Reviews: Prioritizing Outcome Data Availability Over Study Status.

backgroundThe classification of primary studies is a critical methodological step in the conduct of systematic reviews. The current Cochrane approach categorizes studies as 'included', 'excluded', 'ongoing' or 'awaiting classification', primarily based on study eligibility and completion status. However, the concept of an 'ongoing' clinical trial is itself poorly defined across registries and methodological guidelines, introducing a layer of subjectivity that undermines reproducibility.

methodsWe propose a revised classification framework that replaces study status with outcome data availability as the primary classification criterion.

resultsThe proposed framework introduces three changes: (1) splitting the 'included studies' category into 'included studies with analysable outcome data' and 'included studies without analysable outcome data'; (2) eliminating the 'ongoing studies' category, whose function is absorbed by the two proposed categories; and (3) restricting 'awaiting classification' exclusively to studies where eligibility could not be determined.

conclusionThis framework makes more explicit how many eligible studies could not contribute to outcome analysis due to reporting-related problems, thereby increasing transparency and reducing ambiguity in the categorization process. Future empirical studies measuring inter-rater reliability and the operational precision of the proposed categories are needed to validate this proposal.