Psychometric properties of modified 10-item Medication Adherence Scale for cancer patients receiving chemotherapy: Self-report scale validation study

Abstract

Purpose

The 10-item Medication Adherence Rating Scale (MARS-10) is a validated, self-report tool used to assess adherence to chronic illnesses due to its applicability. However, its psychometric properties have not been evaluated among cancer patients receiving chemotherapy. This study aimed to determine the psychometric properties of the modified MARS-10 in this population.

Methods

A cross-sectional analytic study was conducted on adults receiving cancer chemotherapy from April to May 2022. Confirmatory factor analysis was used to validate the scale. The internal consistency was determined using composite reliability. Convergent and discriminant validity of the constructs were measured by the average variance extracted and the Heterotrait-Monotrait correlation ratio, respectively. Statistical significance was declared as p-value < 0.05.

Results

Three hundred (n = 300) adults receiving cancer chemotherapy were enrolled in the study. There was a significant difference between the higher and lower adherence scores, t (299) = 95.84, p < 0.001. The four constructs explained 66.6% of the total variance. The composite reliability of constructs one (0.79), two (0.66), three (0.66), and four (0.66) was in the acceptable to good range. The extracted mean-variance was more than 0.50, and the Heterotrait-Monotrait correlation ratio ranged from 0.31–0.83 for all constructs.

Conclusion

This study has established the internal psychometric properties of the modified 10-item Medication Adherence Rating Scale. Therefore, this modified scale is a valuable tool for researchers and has important implications for oncology health promotion, and policymakers where direct adherence measurement to cancer chemotherapy is challenging.