['Informed consent' and prerandomization].

: The usual procedure in randomised controlled trials is to obtain informed consent first, after which participants can be randomised. The reversal of the order, first randomisation and then informed consent, is called pre-randomisation (Zelen design). In the Netherlands, there is discussion as to whether pre-randomisation should be allowed in medical research. Full informed consent regarding the design of the investigation may lead to unwanted loss of distinction between the experimental and control groups, thus reducing the internal validity of the investigation. A possible solution could be to include, in the informed consent procedure, the statement that certain information has been withheld because revealing it now would make the investigation useless, but that it will be revealed to all participants afterwards and that the study design was approved by the medical ethics committee. In this way, the advantage of the enhanced internal validity of the pre-randomisation design is retained while simultaneously keeping intact the sequence of first informed consent and then randomisation.