It is well established that random assignment between experimental treatment and control arms is the gold standard in clinical trials to minimise differences between the groups being compared and safeguard against bias. There is, however, a fear that such random allocation may not accord with patients’ preferences for the intervention or treatment, thereby compromising trial validity. It is possible that patients may resent not receiving their treatment of choice, and their negative attitude may lead to non-adherence to treatment or affect outcomes in some other way. Consequently, one option for trial designers is to include patient preference arms, whereby patients with no treatment preference are randomly allocated to experimental and control arms, while patients expressing a treatment preference are allocated to receive their preferred treatment.¹

Most of the debate about preference arms has focused on issues concerning increases in the sample size required, the types and stages of randomised design, and how to compare the groups. Ethical issues also arise, leading to concerns about those with strong treatment preferences being included in studies in the first place, especially those in which randomisation takes place irrespective of patients’ elicited preferences (that is, to measure whether those who received their preferred treatment, or not, differed from the no preference groups). There is less information about how doctors’ preferences for treatment influence their …