Introduction. Questionnaires are accessible, inexpensive and simple method for assessing medication adherence. One of the most commonly used questionnaires is Morisky Medication Adherence Scale (MMAS), in 4-item and upgraded 8-item version.
Objective. The aim of our study was systematic review of the studies that examined the reliability and validity of MMAS.
Methods. We searched database Medline up to 27th February 2019. With determined search profile we got 998 studies. The search was limited to articles in English that examined the reliability and/or validity of questionnaire MMAS. We used PRISMA guidelines.
Results. We included 181 studies. The reliability was tested using measure of internal consistency, which was assessed using Cronbach's α (48 studies) and with test-retest method (17 studies). Coefficient α ranged from 0,32 – 0,73 (MMAS-4) and from 0,31 – 0,84 (MMAS-8). Results for test-retest reliability, that measures stability of the score over time demonstrated good to excellent stability over time for the MMAS-8 and poor for the MMAS-4. Content validity was provided through following forward/backward translation guidelines and with testing linguistic and cultural adequacy (25 studies). Convergent validity (17 studies) was confirmed with good correlation between both versions of the MMAS and positive correlation with other methods for measuring adherence. The MMAS factorial validity (28 studies) demonstrated that MMAS-4 is one-dimensional scale. The same they demonstrated in 50 % studies for the MMAS-8. Known group validity was tested in 15 studies. In 80 % studies was demonstrated that MMAS-8 is able to differentiate between patients whose disease is controlled and whose is not. Concurrent validity was established in 39 studies. The scale demonstrated low to moderate validity when provided results were correlated with objective methods. Better results were demonstrated when provided results were correlated with others subjective adherence measures. Predictive validity was established in 117 studies. Although they demonstrated statistically significant association between adherence and health outcomes in 80 % studies for both versions of the MMAS, the association was low to moderate. Diagnostic accuracy was also low to moderate.
Conclusion. The MMAS demonstrates acceptable reliability and validity for different translations and health conditions.
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