Translation and validation of the Chinese version of the general medication adherence scale (GMAS) in patients with chronic illness

OBJECTIVE: To translate the English version of general medication adherence scale (GMAS) into a Chinese version and test its reliability and validity in Chinese patients with chronic diseases.

METHODS: After translating the original English version into Chinese (GMAS-C) following the forward-backward translation and expert review procedure, we conducted a pilot study among 10 chronic disease patients. Each patient took about 10 min to complete the scale and was asked about the difficulty of understanding or filling the scale. Then a total of 312 patients aged 18 years or older with chronic illness were selected from the outpatient departments of two tertiary hospitals and a community center in Tianjin from April 2019 to May 2020 by convenience sampling. Cronbach's α coefficient, item-total correlation and test-retest reliability were used to evaluate the scale reliability; expert evaluation method was used to evaluate the content validity of the scale; and exploratory factor analysis, confirmatory factor analysis, and known group validity were used to evaluate the construct validity of the scale.

RESULTS: As a result of the adaptation process, the GMAS-C's structure was determined. It included 3 dimensions and 11 items and was reliable and valid for Chinese patients with chronic diseases. Total Cronbach's α coefficient of the scale was 0.781 and test-retest reliability coefficient was 0.883 after two weeks. The item-level content validity indexes (CVIs) were ≥ 0.78 for all items. A Kaiser-Meyer-Olkin test and Bartlett' test of sphericity test indicated that the sample met the requirements of factor analysis. Exploratory factor analysis extracted three factors with eigenvalue >1, and 60% of the total variance was explained by three-factor solution. Confirmatory factor analysis showed acceptable fit indices (χ2/df = 1.58, IFI = 0.96, TLI = 0.94, CFI = 0.96 and RMSEA = 0.05).

CONCLUSIONS: The GMAS-C demonstrates satisfactory reliability and validity. This scale can be a clinically useful tool to identify the levels of medication adherence and possible barriers for adherence of the medication regime in patients with chronic diseases.