Psychometric Evaluation of the Medication Adherence Report Scale in Caregivers of Low-income, Urban, African American Children with Poorly Controlled Asthma

Objective: Accurately assessing asthma medication usage among low-income, urban, African American children is essential to reduce asthma health disparities. The purpose of this study was to examine the factor structure of the five-item Medication Adherence Report Scale (MARS), in a sample of caregivers of low-income, urban, African American youth with poorly controlled asthma.

Method: Using baseline data from a randomized clinical trial evaluating the efficacy of an environmental control educational intervention, confirmatory factor analysis (CFA) was conducted to ascertain the MARS factor structure. Construct validity was assessed using a regression model inclusive of caregiver-reported medication adherence, Asthma Medication Ratio (AMR), asthma control, and caregiver perception of asthma control as predictors of the MARS.

Results: Caregivers were female (97%) and 27.4% had an annual income under $10,000. The mean MARS score was 21.88 ± 3.33 out of a possible range of 5-25, representing high adherence. Confirmatory factor analysis indicated that a five-item one-factor model marginally fit the data based on the fit indices: (5) = 31.71,  < 0.001; RMSEA ≤ 0.161; CFI = 0.986; TLI = 0.971; and WRMR = 0.979. The MARS was associated with another caregiver-reported measure of medication adherence but not associated with AMR, asthma control, or caregiver perception of asthma control.

Conclusions: The MARS demonstrated marginal fit in CFA and may not be clinically indicated in light of the lack of associations with objective measures of asthma medication adherence and asthma control.