A critique of the double-blind clinical trial. Part 2.

The randomized, double-blind study is generally regarded as the gold standard of clinical drug trials. Bias can occur as a result of the blinding procedure itself, but discussions of this type of bias have been few and far between. This article continues with a detailed discussion of such blinding errors, which can obscure genuine drug effects and be of a sufficient magnitude as to generate false-negative results. Uncritical blinding in clinical studies should therefore be questioned.