Methods of quality control and of continuous audit procedures for controlled clinical trials.

The success of any cooperative clinical trial is dependent on assuring that the data collected are of good quality. This requires that an extensive and detailed program be developed for assuring good quality performance of all participating centers. Procedures for monitoring the clinical centers and procedures for monitoring or assuring quality of data handling and processing in the coordinating center, i.e., procedures for monitoring the coordinating center, are discussed. The procedures described are based on experience in the Diabetic Retinopathy Study, which is completing data collection, and a new study, the Early Treatment for Diabetic Retinopathy Study, which is in the planning phase. Some of the principles will apply to any participating unit. As in all aspects of clinical trials, a quality control program requires attention to detail and careful planning and vigilance on the part of all participants.