Audit of Diabetes-Dependent Quality of Life (ADDQoL) [Chinese Version for Singapore] questionnaire: reliability and validity among Singaporeans with type 2 diabetes mellitus

Swee Sung Soon, Su Yen Goh, Yong Mong Bee, Jiat Ling Poon, Shu Chuen Li, Julian Thumboo, Hwee Lin Wee
Applied Health Economics and Health Policy 2010, 8 (4): 239-49

BACKGROUND: The Audit of Diabetes-Dependent Quality of Life (ADDQoL) questionnaire is an individualized instrument that measures the impact of diabetes mellitus on quality of life (QOL). With the worldwide increase in the number of Chinese people diagnosed with diabetes, we anticipated that a Chinese-language version of the ADDQoL would be urgently needed.

OBJECTIVE: To evaluate the reliability and validity of the ADDQoL (Chinese version for Singapore) among Chinese-speaking Singaporeans with type 2 diabetes mellitus (T2DM).

METHODS: Chinese versions of the ADDQoL, EuroQoL-Visual Analogue Scale (EQ-VAS), EQ-5D and SF-6D were administered to Chinese-speaking participants with T2DM (aged > or =21 years) at a tertiary acute-care hospital by convenience sampling. The ADDQoL was assessed for the following: internal consistency (Cronbach's alpha); test-retest reliability (intraclass correlation coefficient [ICC]); factor structure; known-groups validity (insulin requiring vs non-insulin requiring, with vs without diabetes-related complications, overweight/obese vs not overweight/obese); and convergent and divergent validity (with EQ-VAS, EQ-5D and SF-6D). The usefulness of weighting and 'not applicable' (NA) options (key features of ADDQoL) were also evaluated.

RESULTS: In 88 participants (58% male, mean [SD] age 56.6 [11.74] years), the mean (SD) ADDQoL average weighted impact (AWI) score was -2.613 (1.899). Cronbach's alpha was 0.941 and the ICC was 0.955 (95% CI 0.812, 0.990). In confirmatory factor analysis, the hypothesized one-factor solution was supported. ADDQoL AWI scores correlated strongly with ADDQoL diabetes-dependent global QOL scores (Spearman's rank correlation coefficient [r(s)] = 0.5983) and weakly with generic measures (r(s) = -0.028 for ADDQoL present global QOL scores, 0.310 for EQ-VAS, 0.164 for EQ-5D and 0.281 for SF-6D). Participants who required insulin, those with diabetes-related complications and those who were overweight/obese reported lower AWI scores, but the differences were not statistically significant. Importance scores of zero were assigned 1-28% of the time and the NA options were selected 3-49% of the time.

CONCLUSIONS: The ADDQoL is reliable and probably valid for assessing QOL among Chinese-speaking Singaporeans with T2DM, although known-groups validity warrants further investigation.

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