Patients' evaluation of informed consent to postponed information: cohort study.

Fundamental bias can be introduced in randomised trials if patients cannot be masked for the allocated strategy and assess subjective outcomes. In such a trial, on the effectiveness of outreach stroke care in addition to standard care, we masked patients by modifying the informed consent procedure. Before discharge home we informed patients that we were studying their needs six months after discharge; we could not inform about an additional research question because that would affect the results; this question entailed no risk and would be clarified after follow up; and the ethics committee approved this study. After we got consent we randomised patients. We informed patients in the intervention group about the outreach care programme and asked them to participate, but we kept them ignorant that we were studying the programme for effectiveness. Controls received no further information. After follow up, we sent all participants a letter with the postponed information on the additional research question, randomisation, and the reasons why patients did not receive this information during recruitment. Several arguments can be raised against this modification. Firstly, it would lead to a high rate of patients who decline to participate. Secondly, it would lead to a decreased trust of patients in their treating doctors; thirdly, it would lead to less willingness to participate in future studies. Fourthly, this modified procedure would not treat patients with respect. The first three arguments contain empirical claims that were studied.