Validity and reliability of an instrument for assessing health-related quality of life and treatment preferences: the Insulin Delivery System Rating Questionnaire.

OBJECTIVE: To provide a preliminary assessment of the validity and reliability of a new measure of health-related quality of life (HRQOL) and treatment preference for insulin delivery systems. RESEARCH DESIGN AND METHODS: Study participants were 197 adults with type 1 or type 2 diabetes who completed the Insulin Delivery System Rating Questionnaire (IDSRQ), a self-administered questionnaire developed for this study. The IDSRQ assessed patient perceptions of treatment satisfaction, impact of treatment on daily activities, clinical efficacy, diabetes-related worries and social burdens, psychological well-being, and overall treatment system preference of patients using continuous subcutaneous insulin infusion (CSII) and multiple daily injections (MDI).
RESULTS: The IDSRQ subscales had acceptable reliability (alpha = 0.67-0.92, median 0.82) and test-retest correlations (intraclass correlation coefficient 0.67-0.94, median 0.88). Floor effects (0-10%, median 0%) and ceiling effects (0-18%, median 4%) were minimal. There were statistically significant differences (P < 0.05) between patients using CSII and MDI on all IDSRQ subscales except psychological well-being (P = 0.096); differences in means were 0.3-1.4 SD units (median 0.9). Multiple regression analysis (controlling for age, sex, and type of diabetes) showed that treatment satisfaction, perceived clinical efficacy, and psychological well-being were independently associated with overall treatment preference and accounted for half of the difference in preference between CSII and MDI patients.
CONCLUSIONS: Preliminary findings suggest that the IDSRQ is a valid and reliable measure of HRQOL and treatment preferences for insulin delivery systems. The subscales are comprehensive, sensitive to differences in user populations, and account for most of the preference for a particular insulin delivery system.