Aims: This study aimed to establish the psychometric properties of a questionnaire measure of patients' adherence to medications to elicit patients' report of medication use in a variety of clinical samples. The reliability and validity were assessed in patients with hypertension. Additional analyses were performed on other patient groups.
Methods: Using a cross-sectional study design, a 10-item version of the Medication Adherence Report Scale (©Professor Rob Horne) was piloted in two samples of patients receiving treatment for hypertension (n = 50 + 178), asthma (n = 100) or diabetes (n = 100) at hospital outpatient or community clinics in London and the south-east of England. Following principal components analysis, five items were retained to form MARS-5 (©Professor Rob Horne). Evaluation comprised internal reliability, test-retest reliability, criterion-related validity (relationship with blood pressure control) and construct validity (relationship with patients' beliefs about medicines).
Results: The MARS-5 demonstrated acceptable reliability (internal and test-retest) and validity (criterion-related and construct validity) in these patient groups. Internal reliability (Cronbach's α) ranged from 0.67 to 0.89 across all patient groups; test-retest reliability (Pearson's r) was 0.97 in hypertension. Criterion-related validity was established with more adherent hypertension patients showing better blood-pressure control (χ2 = 4.24, df = 1, P < .05). Construct validity with beliefs about medicines was demonstrated with higher adherence associated with stronger beliefs in treatment necessity and lower treatment concerns.
Conclusions: The MARS-5 performed well on several psychometric indicators in this study. It shows promise as an effective self-report tool for measuring patients' reports of their medication use across a range of health conditions.
Keywords: MARS-5; Medication Adherence Report Scale; adherence; self-report; validation.
© 2019 The Authors. British Journal of Clinical Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.