Inconsistent reporting of surrogate outcomes in randomised clinical trials: cohort study

OBJECTIVE: To assess if authors of randomised clinical trials convey the fact that they have used surrogate outcomes and discussed their validity. DESIGN: Cohort study. SETTING: Six major general medical journals. PARTICIPANTS: Randomised clinical trials published in 2005 and 2006 that used a surrogate as a primary outcome. RESULTS: Of 626 published randomised clinical trials, 109 (17%) used a surrogate as a primary outcome. Of these trials, 62 (57%, 95% confidence interval 47% to 67%) clearly reported that the primary outcome was a surrogate. Only 38 (35%, 26% to 45%) also discussed the validity of the surrogate. CONCLUSION: Only about one third of authors of randomised clinical trials that used a surrogate as a primary outcome reported adequately on the surrogate. Better reporting is needed.