Physician consent and researchers' access to patients.

Institutional review boards may require that researchers obtain permission from a patient's physician before initiating patient contact. We describe how this requirement affected a study of head injuries. Physicians denied study participation to 8% of 243 subjects; 9% of 126 physicians denied contact with at least one subject. Most physicians responded within ten days, although seven required more than a month to respond. Delays in reaching potential subjects compromise some clinical research protocols. Physicians may refuse permission for some patients, introducing selection biases. Our study did not detect such an effect, but investigators should be alert to such problems in their own research.