• Louis S Matza, Kristina S Yu-Isenberg, Karin S Coyne, Jinhee Park, Jessica Wakefield, Elizabeth P Skinner, and Ruth Quillian Wolever.
• Center for Health Outcomes Research, United BioSource Corporation,Bethesda, MD, USA. louis.matza@unitedbiosource.com
• Curr Med Res Opin. 2008 Nov 1; 24 (11): 319732063197-206.

ObjectiveThis study examined the psychometric properties of the ASK-20 questionnaire, which was developed to assess barriers to medication adherence.Research Design And MethodsPatients with asthma, diabetes, and congestive heart failure were recruited from a university medical center. Participants in this convenience sample completed the ASK-20 questionnaire and other questionnaires. Approximately one-third of participants were randomized to a 2-week retest administration. Analyses examined the reliability and validity of the ASK-20.ResultsA total of 112 patients participated (75.9% female; mean age = 46.7 years). The ASK-20 had good internal consistency reliability (Cronbach's alpha = 0.76) and test-retest reliability (0.80). Concurrent validity was demonstrated through significant correlations with the Morisky Medication Adherence Scale (r = -0.61, p < 0.001), condition-specific measures, and the SF-12 Mental Component Summary score (r = -0.40, p < 0.001). The correlation of the ASK-20 with proportion of days covered by filled medication prescriptions in the past 6 months (based on pharmacy claims) was relatively weak (r = -0.13), but in the expected direction. The ASK-20 total score significantly discriminated among groups of patients who differed in self-reported indicators including the Morisky score; missing a medication dose in the past week; number of days medication was not taken as directed; and treatment satisfaction.ConclusionThe ASK-20 demonstrated adequate reliability and validity, and it may be a useful measure of barriers to treatment adherence across a spectrum of chronic diseases. Limitations related to scale construction, lack of longitudinal data, and item characteristics are discussed.

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