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.