Comparison of anonymous versus nonanonymous responses to a medication adherence questionnaire in patients with Parkinson’s disease

Purpose: Adherence to medication can be assessed by various self-report questionnaires. One could hypothesize that survey respondents tend to answer questions in a manner that will be viewed favorably by others. We aimed to answer if anonymous and nonanonymous responses to a questionnaire on medication adherence differ. Patients and methods: Adherence was assessed with the German Stendal Adherence with Medication Score (SAMS), which includes 18 questions with responses based on a 5-point Likert scale. Anonymous data from 40 subjects were collected during a symposium for patients with Parkinson's disease (PD), and nonanonymous data were obtained from 40 outpatient-clinic PD patients at the Department of Neurology. Results: The two groups (anonymous self-reported questionnaire and nonanonymous) did not differ in terms of demographical characteristics and the SAMS sum score. However, anonymously collected data showed significant higher scoring for the item 6 ("Do you forget your medications?") than the data collected nonanonymously (P=0.017). All other items of the SAMS did not significantly differ between both groups. Conclusion: Overall assessment of adherence does not depend on whether the patient remains anonymous or not. There seems to be no relevant social desirability bias in nonanonymous responses.