Informed consent for clinical trials: In search of the "best" method

Objective: To review the literature on comparisons between different method s of obtaining informed consent for clinical trials. Design: Eight hundred and twelve articles were traced, in the process of conducting a systematic review of the ethics of clinical trials, by searching a number of sources: bibliographic databases (Medline, Psychlit and BIDS science and social scie nce indices), hand searches, personal contacts, an original collection and a systematic follow-up of reference lists. Fourteen research reports were f ound which provided comparative data on different methods of obtaining info rmed consent. Eleven of these used a randomised design. Studies were classi fied according to three outcome measures (anxiety, consent rate and underst anding). Results: The results of the various studies suggest that giving pe ople more information and more time to reflect tends to be associated with a lower consent rate. There seems to be an optimal level of information abo ut side-effects such that patients are not overburdened by detail, while gr asping the most important risks. More information in general is associated with greater awareness of the research nature of the trial, voluntariness o f participation, right to withdraw and (available) alternative treatments. This result does not, however, er;rend to explanations of the concept of ra ndomisation on which the literature is contradictory - sometimes more infor mation is associated with increased understanding of the concept and someti mes it is not. Although divulging less information seems to be associated w ith less anxiety, there is evidence of an interaction with knowledge - high levels of knowledge are significantly associated with less anxiety, irresp ective of consent method. The more that patients know before they are invit ed to participate in a trial, the better equipped they are to cope with the informed consent procedure. Conclusion: There is some evidence to suggest that there is an optimal amount of information which enhances patient under standing and which might, in turn, reduce anxiety. However, the studies wer e not altogether conclusive. More work needs to be carried out, especially on public understanding of science and on how different ways of explaining scientific concepts affect that understanding. (C) 1998 Published by Elsevi er Science Ltd. All rights reserved.