Psychometric evaluation of a self-medication assessment tool in an elderly population.

BACKGROUND Most community-dwelling older adults are engaged in medication self-management activities. Deviation in these activities can lead to adverse outcomes for patients and an increased burden on the health care system. Successful medication self-management involves a complex interaction among cognitive, functional, and psychosocial variables. Several assessment instruments have been developed, but there remains a need for an effective and comprehensive tool. OBJECTIVE To evaluate the psychometric properties (inter-rater reliability, test-retest reliability, and validity), as well as the usability, of the Self-Medication Assessment Tool (SMAT), an instrument designed to measure elderly patients' ability to manage their medications. METHODS The study enrolled patients 65 years of age or older who were living independently and were admitted to family medicine beds in a community hospital in eastern Canada. Three subsamples of the population were identified. The inter-rater reliability group was videotaped and scored independently by 2 pharmacists. The test-retest reliability group was tested with the SMAT and was retested with the same tool a week later. The usability group was interviewed after using the SMAT to determine their satisfaction. Standard neuropsychological measures (Cognitive Competency Test, clock-drawing test, and Mini Mental State Examination [MMSE]) were used to determine convergent and divergent validity. Pill counts, refill rates, and use of adherence aids or reminders before study enrolment were used as measures of concurrent validity. RESULTS A total of 121 patients (mean age 81.5 years) were enrolled. The scales of the SMAT were determined to have good internal consistency and high inter-rater and test-retest reliability. Convergent validity was evidenced by the high positive correlation between the functional scale of the SMAT and the results of the clock-drawing and Cognitive Competency tests (p < 0.01) and between the cognitive and recall scales of the SMAT and the results of the clock-drawing test (p < 0.05), the MMSE (p < 0.01), and the Cognitive Competency Test (p < 0.01). Patients reported being highly satisfied with their experience. CONCLUSION The SMAT is a practical, reliable, comprehensive instrument with demonstrated convergent validity, strong patient acceptability, and various internally consistent scales that assess multiple dimensions of elderly patients' ability to self-manage their medications. Further testing is required to show that the SMAT correlates with medication adherence.