Cross-cultural adaptation of the simple Chinese version of the medication adherence reasons scale in patients undergoing adjuvant endocrine therapy for breast cancer

Adjuvant endocrine therapy (AET) is essential for improving survival and reducing mortality and recurrence rates in breast cancer (BrCa) patients. However, the adherence to AET among BrCa patients is poor, and there is no scale to measure adherence to AET or the reasons for non-adherence among BrCa patients in mainland China. The aim of this study was to assess the psychometric properties of the simple Chinese version of the Medication Adherence Reasons (MAR) scale in BrCa patients undergoing AET. This study utilized a cross-sectional research design with two phases: (1) translation and cross-cultural adaptation of the original English version of the MAR scale into simple Chinese and (2) validation of the simple Chinese version of the MAR scale (s-ChMAR scale) in BrCa patients. Instrument assessments included content validity, face validity, item analysis, construct validity, criterion-related validity and reliability testing. This study recruited participants using convenience sampling to investigate adherence to AET among BrCa patients. Inclusion criteria were: (a) female, (b) aged 18 years or older, (c) diagnosed with Stage I to III BrCa, (d) completed primary treatment for hormone receptor-positive BrCa and had been on AET for more than six months but less than five years, (e) proficient in Mandarin, and (f) provided informed consent. Exclusion criteria included psychiatric illness, cognitive impairment, or a diagnosis of another cancer type. The sample size for exploratory factor analysis (EFA) was determined based on a ratio of five to ten participants per scale item to ensure sufficient statistical power. Data were collected from a sample of 325 participants who received AET for over six months. All the items had a content validity index (CVI) of more than 0.80. Regarding construct validity, the s-ChMAR scale fit a four-dimensional model, the same as the original MAR scale tested in asthma patients. The s-ChMAR scale had good internal reliability (Cronbach's α = 0.896) and good stability (ICC = 0.837). In terms of quantifying non-adherence, the s-ChMAR scale identified a non-adherent participant rate of over 50%. The study findings support the reliability and validity of the s-ChMAR scale in measuring the non-adherence of Chinese BrCa patients to AET.