Improving self-report measures of medication non-adherence using a cheating detection extension of the randomised-response-technique.

Medication non-adherence is a serious problem for medical research and clinical practice. Self-reports are only moderately valid, and objective methods are cumbersome and expensive to administer. We sought to improve self-reports of medication non-adherence using a cheating detection extension of the randomised-response-technique (RRT). This RRT variant encourages more honest responses by offering interviewees a higher degree of anonymity while simultaneously allowing us to estimate the proportion of respondents disobeying the RRT instructions. The 597 patients were asked to report their lifetime prevalence of medication non-adherence under one of two different questioning procedures, direct questioning or randomised-response. When questioned directly, only 20.9% of patients admitted to intentional medication non-adherent behaviour, as opposed to 32.7% of patients under RRT conditions. Additionally, the cheating detection extension revealed a significant proportion of patients (47.1%) disobeying the instructions in the RRT condition. Assuming that either none or all of them were non-adherent, a lower and upper bound of 32.7% and 79.8%, respectively, could be estimated for the lifetime prevalence of non-adherent behaviour. The results demonstrate that self-report measures as well as traditional variants of the RRT, which do not take cheating into account, may provide considerably distorted estimates of the prevalence of medication non-adherence.