Testing the psychometric properties of the Medication Adherence Scale in patients with heart failure.

OBJECTIVE: Many factors may contribute to medication nonadherence in heart failure (HF), but no standard measure exists to evaluate factors associated with nonadherence. To fill this gap, we developed the Medication Adherence Scale (MAS) and tested its reliability and validity in patients with HF. METHOD: Questionnaire data were collected from 100 patients with HF at baseline using the MAS, and objective adherence data were collected for 3 consecutive months using the Medication Event Monitoring System. RESULTS: Principal component analysis yielded three factors that explained 63% of the variance in medication adherence: knowledge, attitudes, and barriers to medication adherence. Cronbach's alphas for these subscales ranged from .75 to .94, which supported their internal consistency. The Spearman rho correlation coefficients between the Medication Event Monitoring System and Knowledge, Attitudes, and Barriers scores were .25 to .31 (P < .05), demonstrating support for construct validity. CONCLUSION: These results support the reliability and validity of the MAS as a measure of knowledge, attitudes, and barriers of medication adherence. [ABSTRACT FROM AUTHOR]