Type-II error rates (beta errors) of randomized trials in orthopaedic trauma

Background: Although an investigator may limit bias through randomization, concealment of patient allocation, and blinding, the results of randomized trials may be less convincing when the sample size is not sufficiently larg e to reveal a true difference between treatment groups. When the sample siz e is small, randomized trials are subject to beta errors (type-II errors)-t hat is, the probability of concluding that no difference between treatment groups exists when, in fact, there is a difference. The purpose of this stu dy of randomized trials involving fracture care published between 1968 and 1999 was twofold: (1) to evaluate type-II error rates and study power (1-be ta) for the primary outcomes and (2) to identify whether investigators clea rly identified the primary and secondary outcomes. Methods: To be eligible, studies were required to (1) be published in Engli sh, (2) be described as a randomized trial, (3) involve the care of adult p atients with fractures, treated either operatively or nonoperatively, and ( 4) contain sufficient outcome information to enable study power to be calcu lated. Computer database searches were performed independently by two inves tigators to identify all potentially relevant study titles. Additional stra tegies to identify articles included (1) hand searches of selected orthopae dic journals from 1989 to 1999, (2) searches of the bibliographies of poten tially relevant articles, and (3) review by content experts to identify mis sing studies. For each study, a standard power calculation was performed on the primary and secondary outcomes. For those studies in which the primary outcome was not explicitly reported, the most clinically relevant measure was chosen by consensus. Acceptable study power was agreed a priori to be g reater than or equal to 80% (type-I error of less than or equal to0.20). Results: We identified 620 potentially relevant citations from MEDLINE, of which only 187 were potentially eligible. We identified nine more articles with other searches, and application of the eligibility criteria to the 196 articles eliminated seventy-nine. Thus, we analyzed 117 studies in which a total of 19,942 patients with orthopaedic trauma had been randomized. Samp le sizes ranged from ten to 662 patients (mean and standard deviation, 95 /- 79 patients). The majority (34%) of trials involved the treatment of hip fractures. The mean overall study power among the 117 trials was 24.65% (r ange, 2% to 99%). The type-II error rate for primary outcomes was 90.52%. Conclusions: Mean type-II error rates in the orthopaedic trauma trials that we analyzed exceeded accepted standards. Investigators can reduce type-II error rates by performing power and sample-size calculations prior to condu cting a trial.