Reliability and validity of the Medication Adherence Rating Scale in a cohort of patients with schizophrenia from Nigeria

Abstract Introduction Assessing adherence in schizophrenia facilitates interventions that optimize outcomes. Adherence rating questionnaires are feasible and non-intrusive; however, no validated measure exists in sub-Saharan Africa. We aimed to assess the psychometric properties of the 10-item Medication Adherence Rating Scale (MARS). Methods This was a cross-sectional study of a cohort of patients with schizophrenia (n=230). A sociodemographic questionnaire, the Mini International Neuropsychiatric Interview (MINI), Positive and Negative Syndrome Scale (PANSS), Scale for the Unawareness of Mental Disorder (SUMD) and the MARS were all administered by an interviewer. Results The MARS demonstrated good reliability (Cronbach’s alpha: 0.76). The scale was reducible to a 3-factor construct (1 – medication adherence behavior, 2 – attitude to taking medications, and 3 – negative side effects and attitude to psychotropics), with significant though weak external validity in relation to psychopathology (p<0.001) and insight (p<0.001). The first factor showed good internal consistency (α=0.80), comprising six items that could serve as a reliable proxy measure of adherence in place of the MARS Conclusion The MARS demonstrated fair psychometric characteristics in assessing adherence in patients with schizophrenia in this cohort. The scale may be useful in the dimensional assessment of medication adherence for schizophrenia in sub-Saharan African settings.