Psychometric properties of the 8-item Morisky Medication Adherence Scale in patients taking warfarin

Ye Wang; Ming Chai Kong; Yu Ko

doi:10.1160/TH12-05-0368

Thrombosis and Haemostasis, Table of Contents

Thromb Haemost 2012; 108(04): 789-795
DOI: 10.1160/TH12-05-0368

New Technologies, Diagnostic Tools and Drugs

Schattauer GmbH

Psychometric properties of the 8-item Morisky Medication Adherence Scale in patients taking warfarin

Ye Wang

¹Department of Pharmacy, Faculty of Science, National University of Singapore, Singapore

,

Ming Chai Kong

²Department of Pharmacy, Singapore General Hospital, Singapore

,

Yu Ko

¹Department of Pharmacy, Faculty of Science, National University of Singapore, Singapore

› Author Affiliations

Abstract

Summary

There is no patient-reported medication adherence measure that has been validated in Singapore. This study aimed to validate the 8-item Morisky Medication Adherence Scale (MMAS) in patients taking warfarin in Singapore. A cross-sectional survey was conducted in a convenience sample of 151 patients taking warfarin at an anticoagulation clinic in 2011. Respondents completed the MMAS in English or Chinese depending on their preference. The MMAS had a Cronbach′s alpha of 0.56 and good criterion-related validity as the scale scores were associated with warfarin refill rates (p = 0.04). Respondents with higher MMAS scores were found to have a higher percentage of International Normalised Ratios (INRs) within the therapeutic range (p = 0.01), higher adherence to diet recommendations (p = 0.02), and less perceived difficulty in taking all medications (p < 0.001); they were also more likely to take warfarin at the same time every day (p < 0.001). Confirmatory factor analysis showed that the eight items loaded onto one factor (RMSEA = 0.03). The sensitivity, specificity, positive predictive value and negative predictive value of the MMAS for identifying patients with poor INR control were 73.0%, 35.6%, 49.5% and 60.5%, respectively, using the time in the therapeutic INR range as the gold standard. This study shows that the 8-item MMAS has good validity and moderate reliability in patients taking warfarin. Future research is needed to investigate the scale′s psychometric properties in other patient populations and clinical settings.

Keywords

Morisky Medication Adherence Scale - medication adherence - anticoagulation - warfarin

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References

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