Introduction: Asia will be at the forefront of the current epidemic of diabetes mellitus. Quality of life (QOL) is an important outcome measure in the assessment of diabetes care. However, few QOL instruments are culturally suitable for use in Asian countries. The Audit of Diabetes-Dependent Quality-of-Life (ADDQoL) questionnaire is a third-generation individualised QOL instrument. Individualised instruments such as the ADDQoL have the potential to be useful and less costly alternatives to computerised adaptive testing (CAT), which may not be practical in developing countries.
Objective: To evaluate and validate the ADDQoL questionnaire in English-speaking patients with diabetes in Singapore, a multi-ethnic Asian country.
Methods: The ADDQoL and EQ-5D were administered to English-speaking respondents with type 1 or 2 diabetes (aged > or =18 years) recruited from a tertiary acute-care referral hospital by convenience sampling. The usefulness of the key design features of the ADDQoL were assessed by measuring the number of zero-importance responses, the change in item ranking with and without weighting for importance, and the frequency of utilisation of the 'not applicable' (NA) options. The acceptability, factor structure and internal consistency (Cronbach's alpha) of the ADDQoL were also assessed. Data were subjected to unforced factor analysis with oblimin rotation and then the condition was set to force a one-factor solution. The validity of the ADDQoL was tested with the following hypotheses: those with moderate or severe problems on the EQ-5D would have worse ADDQoL average weighted impact (AWI) scores than those with a perfect health rating on the EQ-5D; those with better Present QOL scores on the ADDQoL would have better EQ-5D utility and visual analogue scale (VAS) scores; on the ADDQoL, AWI scores would correlate better with diabetes-dependent QOL than with Present QOL scores; and female respondents, those who required insulin or had longer duration of known diabetes would have worse ADDQoL AWI scores (known-group validity).
Results: We analysed data from 152 respondents (49% Chinese, 34% Indian; 45% female; mean age 52 years, range 18-80; mean duration of known diabetes 10 years, range 0-62). There were few missing data. Weighted scoring and NA options were shown to be necessary, thus supporting the usefulness of individualised health-related QOL measures. Factor structure of the ADDQoL was supported and internal consistency was high (alpha = 0.94). All hypotheses were fulfilled except for one that was partially fulfilled; respondents with longer duration of known diabetes did not report worse ADDQoL AWI scores.
Conclusions: The ADDQoL is culturally appropriate, valid, reliable and well accepted among Singaporean patients with diabetes. Individualised measures such as the ADDQoL allow one to obtain precise score estimates and may offer developing countries a useful alternative to CAT.