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.