THE DEVELOPMENT OF MEDICATION ADHERENCE SCALE FOR PERSONS WITH CORONARY ARTERY DISEASE

Abstract

This study aimed to develop and test psychometric properties of the new instrument namely the Medication Adherence Scale (MAS). The instrument development composed of seven steps included 1) synthesizing the concept of medication adherence using literature review and consensus of 17 experts through Delphi technique, 2) generating an item pool, 3) determining the format for measurement, 4) reviewing the initial item pool by seven professional experts, 5) conducting preliminary item tryout in 30 persons with CAD, 6) conducting field-test for psychometric property testing in 457 persons with CAD who attended at heart clinic of seven tertiary hospitals in Thailand, and 7) developing scoring and interpretation of the scale score. Data was analyzed by using descriptive statistics, content validity index, Cronbach’s alpha coefficient, confirmatory factor analysis by LISREL, and Pearson product moment correlation. The results showed that the MAS is a self-report, five rating categories Likert-scale format, composed of 25 items covering four constructs; knowing about medication properly (7 items), storing medication appropriately (3 items), self-regulating in taking medication correctly and continuously (11 items), and participating in medication treatment plan (4 items). The MAS was valid and reliable instrument to measure medication adherence for persons with CAD. The MAS had item-content validity index ranged from .86-1.0, and scale-content validity index/average was .99. Cronbach’s alpha reliability was high (α= .81). Test retest reliability was acceptable (r=.62, p<.01). Confirmatory factor analysis fit to the empirical data (X2=533.78, df=244, p=0.00, X2/df=2.19, GFI=0.91, AGFI=0.89, CFI=0.94, RMSEA=0.05).