Objectives: Patient literacy affects many aspects of medication use and may influence the measurement of adherence. The aim of the study is to design and evaluate a medication adherence scale suitable for use across levels of patient literacy.
Methods: The Adherence to Refills and Medications scale (ARMS) was developed, pilot tested, and administered to 435 patients with coronary heart disease in an inner-city primary care clinic. Psychometric evaluation performed overall and by literacy level, included an assessment of internal consistency, test-retest reliability, and factor analysis. Criterion-related validity was evaluated by comparing scores with Morisky's self-reported measure of adherence, medication refill adherence, and blood pressure measurements. Lexile analysis was performed to assess the reading difficulty of the instrument.
Results: The final 12-item scale had high internal consistency overall (Cronbach's alpha = 0.814) and among patients with inadequate (alpha = 0.792) or marginal/adequate literacy skills (alpha = 0.828). Factor analysis yielded two subscales, which pertained to taking medications as prescribed and refilling medications on schedule. The ARMS correlated significantly with the Morisky adherence scale (Spearman's rho = -0.651, P < 0.01), and it correlated more strongly with measures of refill adherence than did the Morisky scale. Patients with low ARMS scores (which indicated better adherence) were significantly more likely to have controlled diastolic blood pressure (P < 0.05), and tended to have better systolic blood pressure control. Lexile analysis demonstrated that the instrument had a favorable reading difficulty level below the eight grade.
Conclusion: The ARMS is a valid and reliable medication adherence scale when used in a chronic disease population, with good performance characteristics even among low-literacy patients.