Inclusion criteria for outcomes of studies not clearly reported in Cochrane systematic reviews.

OBJECTIVES: The objective of this study was to survey how outcomes in recent Cochrane reviews were defined and used for inclusion of studies and how this compares with guidance on preventing outcome reporting bias.

STUDY DESIGN AND SETTING: A survey of Cochrane reviews. We extracted data on the outcomes and how the outcomes were used for inclusion of studies in the review.

RESULTS: We included 52 reviews with a mean of 8.4 (standard deviation, 4.3) outcomes. Of all reviews, 47 (90%) used primary and secondary outcomes as the names for their review's outcomes but without further definition. None reported using a core outcome set. Forty reviews (77%) did not explain if they used outcomes for inclusion of studies, 8 (15%) stated that studies were included if they reported either primary or secondary outcomes, 1 (2%) reported that outcomes were not used for inclusion, and for 3 (6%), this was unclear.

CONCLUSION: In a sample of Cochrane reviews, most reviews did not state if outcomes were used for inclusion of studies. Better explanation of inclusion decisions is needed to be able to understand the risk of outcome reporting bias in a review. Consistent guidance in names and definitions for different types of outcomes used in systematic reviews is needed.