Effect of investigator bias on clinical trials.

Two clinical trials were performed to determine the relative efficacy of tioconazole, a new antifungal agent for treating patients with tinea pedis. One study compared the new agent with a placebo cream and the other with miconazole nitrate, an established effective antifungal agent. The investigators found a much higher "cure" rate for tioconazole when both treatment groups were known to receive active agents than the cure rate for tioconazole found in the placebo-controlled study. These results showed that the expectations of investigators can influence their clinical evaluations. Such bias could also influence the results of clinical trials.