Informed consent as a form of volunteer bias.

Two nontreatment studies of tardive dyskinesia were examined to see if giving or refusing informed consent might bias results. Three prominent psychiatric journals were also reviewed to determine whether the outcome of informed consent procedures was sufficiently well described to permit evaluation of potential bias. The nontreatment studies suggested that the bias created by requiring informed consent may cause both false-positive and false-negative findings. The literature review showed that treatment studies have generally ignored the potential impact of these biases on results. Accurate interpretation of research reports, particularly clinical trials, demands that more attention be given to the process of obtaining and reporting informed consent.