Reporting of eligibility criteria of randomised trials: cohort study comparing trial protocols with subsequent articles

OBJECTIVE To determine whether and how eligibility criteria of participants prespecified in protocols of randomised trials are reported in subsequent articles. DESIGN Cohort study. SETTING Protocols submitted to the ethics committee of a German medical faculty. DATA SOURCES 52 trial protocols and 78 subsequent publications published between 2000 and 2006. MAIN OUTCOME MEASURE Proportion of matching, missing, modified, or newly added eligibility criteria between trial protocols and subsequent publications. RESULTS Differences were found between protocols and subsequent publications for all 52 trials. Information on eligibility criteria was missing in the publications for all 52 trials (100%, 95% confidence interval 93% to 100%), modified for 44 (85%, 72% to 93%), and newly added for 21 (41%, 27% to 55%). The mean number of eligibility criteria for each trial was 25 (range 7-43) and the mean proportion of matching eligibility criteria per trial was 50% (95% confidence interval 44% to 55%, range 13-93). Of 1248 eligibility criteria prespecified in the protocols, 606 (49%, 46% to 51%) were matching in subsequent publications, 479 (38%, 36% to 41%) were missing, and 163 (13%, 11% to 15%) were modified. 51 eligibility criteria were added to publications. Most prespecified eligibility criteria were about comorbidity (42%, 39% to 45%), treatment (20%, 18% to 22%), or type or severity of illness (17%, 15% to 19%). Most of the missing eligibility criteria (96%, 94% to 97%) and modified eligibility criteria (54%, 46% to 62%) suggested broader study populations and most of the added eligibility criteria (86%, 74% to 94%) suggested narrower study populations. CONCLUSIONS Many users of trial information rely on published journal articles. These articles generally do not reflect the exact definition of the study population as prespecified in the protocol. Incomplete or inadequate reporting of eligibility criteria hampers a proper assessment of the applicability of trial results.