Affiliation:
1. Department of Pharmacy Practice, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok, Thailand
2. Sawangdandin Crown Prince Hospital, Sakonnakorn Province, Thailand
3. Department of Pharmacy Administration, Faculty of Pharmaceutical Sciences, Chulalongkorn University
Abstract
Background A self-reporting questionnaire is the most convenient and cheapest way to assess medication adherence. A new 8-item self-reported Morisky Medication Adherence Scale (MMAS) has been developed and has shown better psychometric properties than the original 4-item Morisky scale. Objective To examine the validity, including convergent known-groups and construct validity, and reliability, including internal consistency and test–retest reliability, of the MMAS in Thai patients with type 2 diabetes. Methods The data were derived from a cross-sectional study. In a convenience sample, 303 type 2 diabetic outpatients were interviewed at the General Police Hospital in Bangkok, Thailand, between January and June 2007. Face-to-face interviews included MMAS, medication adherence visual analog scale (MA-VAS), and sociodemographic data. Medical records were reviewed for clinical data such as hemoglobin A1c (A1C) levels. Results Internal consistency reliability was moderate (Cronbach's α = 0.61), whereas the test–retest reliability of the MMAS was excellent (intraclass correlation coefficient = 0.83; p < 0.001). Concerning convergent validity, the MMAS had a high correlation with the 3-item Morisky scale (r = 0.77; p < 0.01) and a medium correlation with the MA-VAS (r = 0.57; p < 0 01). Regarding known-groups validity, a significant association between MMAS and A1C levels was found (χ2 = 6.7; p < 0.05). The sensitivity, specificity, positive predictive value, and negative predictive value of the MMAS were 51%, 64%, 71%, and 43%, respectively. Our factor analysis showed that the MMAS had 3 dimensions including forgetting to take medications, stopping medications when feeling better or worse, and the complexity of the drug regimen. Conclusions The 8-item MMAS can be a tool to aid in assessing medication adherence in diabetes. The poor sensitivity can be improved by increasing the number of the response choices and the cut-off score of the scale and by using specific words in some items. A modified Thai version of the 8-item MMAS may be needed.