Self-care time and rating of health state in people with diabetes: Results from the population-based KORA survey in Germany

Aims: Health-related changes in leisure time are supposed to be implicitly considered by participants of health state valuations. The amount of empirical research on whether respondents in fact include the effects of morbidity on leisure into health state valuations is limited and the results are inconclusive. In this exploratory study, we analyze whether time aspects of diabetes self-care might explain the ratings of the health state (HSR) in addition to the effects of physical and mental health-related quality of life. Methods: Using the data from participants with diagnosed type 2 diabetes in the population-based KORA FF4 study (n=190, 60% Male, mean age 69±10 years), multiple logistic regression models were fitted to explain HSR (good vs. poor) in terms of the SF12 physical and mental component scores, time spent on diabetes self-care and a range of background variables. We assume that if time spent on diabetes self-care competes with other leisure activities and implicitly plays a role in HSR, this additional effect should be seen in regression models. Results: There was no significant association between time spent on diabetes self-care and HSR in models without interaction. Significant interaction term was found between physical score of SF12 and time spent on self-care. In models with interaction self-care time has a small, but significant impact on the HSR. In particular, for a fixed physical score of SF12 value under 40, more time increases the chance to rate the health state as "good", while for physical score value above 40 there is a reverse effect. Conclusions: The additional impact of self-care time on HSR in our sample is small and more complex than a simple linear association. More research is needed on whether inclusion of health-related leisure time changes in the denominator of cost-effectiveness analysis is sufficient.