Minimizing Bias in Randomized Trials: The Importance of Blinding

Psaty and Prentice discuss the importance of blinding of investigators and evaluate whether the absence of investigator blinding may have influenced the results of specific important trials. The effort required to blind investigators and patients increases the cost and complexity of trials. However, unless the outcome such as total mortality can be unambiguously and completely ascertained in a time frame common to the treatments, the large long-term trials that establish standards for drug treatments are so important to the health of the public that every effort, including investigator blinding, should be built into the trial design to produce valid results in studies of the highest reliability and the clearest interpretation.