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A cultural adaptation and validation study of a self-report measure of the extent of and reasons for medication nonadherence among patients with diabetes in Singapore

Authors Liau YW, Cheow C, Leung KTY, Tan H, Low SF, Cheen HHM, Lim WC, Tan LL, Tan JZY, Lee ES, Xu SJ, Tan CYK, Phang JW, Phang JK, Lam MH, Blalock DV, Voils CI, Yap KZ, Kwan YH

Received 21 March 2019

Accepted for publication 27 June 2019

Published 29 July 2019 Volume 2019:13 Pages 1241—1252


Checked for plagiarism Yes

Review by Single anonymous peer review

Peer reviewer comments 2

Editor who approved publication: Professor Qizhi (Cathy) Yao

Yuan Wei Liau,1 Celine Cheow,1 Kenneth Tin Yau Leung,2 Hejing Tan,3 Suat Fern Low,4 Hua Heng McVin Cheen,5 Woan Chyi Lim,6 Li Ling Tan,6 Joyce Zhen Yin Tan,7 Eng Sing Lee,8 Sandra Jialun Xu,9 Corrinne Yong Koon Tan,10 Jie Wen Phang,11 Jie Kie Phang,12 Miao Hui Lam,2 Dan V Blalock,13,14 Corrine I Voils,15,16 Kai Zhen Yap,1 Yu Heng Kwan2,17

1Department of Pharmacy, Faculty of Science, National University of Singapore, Singapore, Singapore; 2Department of Pharmacy, Khoo Teck Puat Hospital, Singapore, Singapore; 3Department of Pharmacy, Woodlands Health Campus, Singapore, Singapore; 4Department of Pharmacy, Yishun Community Hospital, Singapore, Singapore; 5Department of Pharmacy, Singapore General Hospital, Singapore, Singapore; 6Department of Pharmacy, Tan Tock Seng Hospital, Singapore, Singapore; 7Department of Pharmacy, Admiralty Medical Centre, Singapore, Singapore; 8Clinical Research Unit, Family Medicine Development Division, National Healthcare Group Polyclinics, Singapore, Singapore; 9Department of Pharmacy, National Healthcare Group Polyclinics (Hougang), Singapore, Singapore; 10Pharmacy Transformation Office, National Healthcare Group Pharmacy, Singapore, Singapore; 11Department of Pharmacy, Ng Teng Fong General Hospital, Singapore, Singapore; 12Department of Rheumatology and Immunology, Singapore General Hospital, Singapore, Singapore; 13Center of Innovation to Accelerate Discovery and Practice Transformation (ADAPT), Durham Veterans Affairs Health Care System, Durham, NC, USA; 14Department of Psychiatry and Behavioral Sciences, Duke University School of Medicine, Durham, NC, USA; 15Department of Surgery, University of Wisconsin School of Medicine and Public Health, Wisconsin, WI, USA; 16William S Middleton Memorial Veterans Hospital, Wisconsin, WI, USA; 17Program in Health Services and Systems Research, Duke-NUS Medical School, Singapore, Singapore

Background: This self-report measure is a new instrument to measure the extent of and reasons for medication adherence separately. However, few studies have assessed its psychometric properties in diabetic patients and also in Asian populations.
Objectives: To validate this self-report measure in diabetic patients in Singapore.
Methods: We collected data prospectively using a questionnaire among 393 diabetic patients from hospitals in Singapore from July 2018 to January 2019. Using the COnsensus-based Standards for the selection of health Measurement INstruments framework, we assessed face validity, internal consistency, test–retest reliability, structural validity, and measurement error. We tested four a priori hypotheses on correlation of extent score with patient-reported outcome measures to assess construct validity. We examined cross-cultural validity via measurement invariance across gender, age groups, and languages.
Results: We performed cognitive interviews with 30 consenting English-literate, Chinese-literate, and Malay-literate (10 patients per language) diabetic patients (age range 48–76 years, 53% male, disease duration range 1–30 years) and face validity was supported. Among 393 patients (mean age: 59.4±12.2 years, 50.9% female, 52.4% Chinese), we showed moderate internal consistency (Cronbach’s alpha =0.67) and test–retest reliability (intra-class coefficient=0.56 [95% CI 0.37–0.70]). We calculated smallest detectable change as 0.80. We established construct validity by meeting all four hypotheses. We showed structural validity as confirmatory factor analysis confirmed a one-factor model, with excellent fit statistics (Comparative Fit Index=1.0; Tucker-Lewis Index=1.0; Root Mean Square Error of Approximation<0.001; Standardized Root Mean Residuals<0.001). Analysis of cross-cultural validity supported configural invariance model but not metric invariance and scalar invariance model. Caution must be taken against directly comparing extent scores across gender, age groups, and languages.
Conclusion: This self-report measure is valid and reliable in measuring medication adherence in diabetic patients in Singapore.

Keywords: adherence, patient-reported outcome, quality of life, psychometric, singapore, diabetes

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