Further testing of the reliability and validity of the ASK-20 adherence barrier questionnaire in a medical center outpatient population

ABSTRACT

Objective: This study examined the psychometric properties of the ASK-20 questionnaire, which was developed to assess barriers to medication adherence.

Research design and methods: Patients 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.

Results: A 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.

Conclusion: The 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.

Key words: :

• ASK
• Chronic diseases
• Medication adherence
• Reliability
• Treatment adherence
• Treatment persistence
• Validity

Acknowledgements

Declaration of interest: This study was funded by GlaxoSmithKline. The authors thank Linda Duda, Chris Clark, and Shin-Yiing Yeung, of the Duke University Medical Center, for recruitment support and data collection. They also thank Jessica Brewster-Jordan, formerly with United BioSource Corporation, for assistance with literature searching; Karen Malley, Malley Research Programming, Inc., Rockville, MD, for thoughtful statistical programming; Peggy Flowers, GlaxoSmithKline, for her direction and support for the ASK-20 development and validation; and Jodi Shorr, formerly with United BioSource Corporation, Fritz Hamme, United BioSource Corporation, and Julie Meilak, United BioSource Corporation, for production assistance.

Notes

* An interim analysis of some of these data was presented at the 2006 Annual Meeting, October 10–14, of the International Society for Quality of Life Research in Lisbon, Portugal