Validity and reliability of a self-reported measure of antihypertensive medication adherence in Uganda

Abstract

Background: The Morisky Medication Adherence scale (MMAS-8) is a widely used self-reported measure of adherence to antihypertensive medications that has not been validated in hypertensive patients in sub-Saharan Africa. Methods: We carried out a cross-sectional study to examine psychometric properties of a translated MMAS-8 (MMAS-U) in a tertiary care hypertension clinic in Uganda. We administered the MMAS-U to consecutively selected hypertensive adults and used principal factor analysis and Cronbach's alpha to determine its validity and internal consistency respectively. Then we randomly selected one-sixth of participants for a 2-week test-retest telephone interview. Lastly, we used ordinal logistic regression modeling to explore factors associated with levels of medication adherence. Results: Of the 329 participants, 228 (69%) were females, median age of 55 years [Interquartile range (IQR) (46-66)], and median duration of hypertension of 4 years [IQR (2-8)]. The adherence levels were low (MMAS-U score ≤5) in 85%, moderate (MMAS-U score 6-7) in 12% and high (MMAS-U score ≥8) in 3%. The factor analysis of construct validity was good (overall Kaiser's measure of sampling adequacy for residuals of 0.72) and identified unidimensionality of MMAS-U. The internal consistency of MMAS-U was moderate (Cronbach α = 0.65), and test-retest reliability was low (weighted kappa = 0.36; 95% CI -0.01, 0.73). Age of 40 years or greater was associated with low medication adherence (p = 0.02) whereas a family member buying medication for participants (p = 0.02) and purchasing medication from a private clinic (p = 0.02) were associated with high adherence. Conclusion: The Ugandan version of the MMAS-8 (MMAS-U) is a valid and reliable measure of adherence to antihypertensive medication among Ugandan outpatients receiving care at a public tertiary facility. Though the limited supply of medication affected adherence, this easy to use tool can be adapted to assess medication adherence among adults with hypertension in Uganda.