Patients’ understanding of randomised controlled trials depends on their education

Editor—We appreciated Featherstone and Donovan’s report about patients’ perspectives of participation in a randomised controlled trial.¹ We recently investigated the ability of 40 middle aged and elderly caregivers to understand and retain information about randomised controlled trials in patients with Alzheimer’s disease.

Eighteen caregivers were men and 22 women, and their mean age was 64 (SD 6) (range 50-76). They had had a mean of 6 (3) years of schooling (range 5-17), and their mean score in the minimental state examination was 29 (1) (range 25-30). They were given information in a semistructured manner, including information sheets. Twenty eight of them could not explain why placebo, randomisation, and double blind procedures were used. Furthermore, eight of them could not recall anything other than a vague idea of participation in an “experiment” and the possible use of a placebo for some unknown reason. Using a four step scale to rate competency to participate in a randomised controlled trial on the basis of understanding information we found a significant positive correlation between competency and degree of education.

We agree that accurate information does not ensure understanding of the features of randomised controlled trials. Our results are similar to those of Featherstone and Donovan, in that 30% (6/20) of their subjects and 20% (8/40) of ours were unaware of the influence of chance. However, Featherstone and Donovan did not report the degree of education of their subjects. We wonder whether awareness of randomisation and degree of education were correlated in their subjects. We hope that cross cultural studies will contribute further to our hypothesis that the understanding of information based on a scientific standard for obtaining consent to randomised controlled trials is strictly linked to social and cultural background. The large discrepancy between the complexity of methods for randomised controlled trials and the poor education of many potential participants should be highlighted in discussions of issues surrounding informed consent.