@article{HammerschmidtZeitlerGulichetal.2004, author = {Hammerschmidt, Thomas and Zeitler, HP. and Gulich, M. and Leidl, R.}, title = {A Comparison of Different Strategies to Collect Standard Gamble Utilities}, series = {Medical Decision Making}, journal = {Medical Decision Making}, year = {2004}, abstract = {Objective. The authors performed a methodological comparison of the usual standard gamble with methods that could also be used in mailed questionnaires.Methods.Ninety-two diabetic patients valued diabetes-related health states twice. In face-to-face interviews, the authors used an iterative standard gamble (ISG) in which the probabilities were varied in a ping-pong manner and a self-completion method (SC) with top-down titration as search procedure (SC-TD) in 2 independent subsamples of 46 patients. Three months later, all patients received a mailed questionnaire in which the authors used the self-completion method with bottom-up (SCBU) and SC-TD as search procedures.Results.ISG and SCTD showed feasibility and consistency in the interviews. The ISG resulted in significantly higher utilities than the SC-TD. Two thirds of the mailed questionnaires provided useful results indicating some problems of feasibility. Utilities measured by SC-BU and SC-TD did not differ significantly showing procedural invariance. Further, patients indicated ambivalence when given the choice not to definitely state their preferences.Conclusions.The results show that different strategies to collect standard gamble utilities can yield different results. Compared with the usually applied ISG, the SC method is feasible in interviews and provides a consistent alternative that is less costly when used in mailed questionnaires, although its practicability has to be improved in this later setting.}, language = {en} } @article{HammerschmidtZeitlerLeidl2004, author = {Hammerschmidt, Thomas and Zeitler, HP and Leidl, R.}, title = {A utility-theoretic approach to the aggregation of willingness to pay measured in decomposed scenarios: development and empirical test.}, series = {Health Econ}, journal = {Health Econ}, year = {2004}, abstract = {For cost-benefit analysis, health technologies with multiple effects should be valued in a single scenario by a holistic willingness-to-pay (WTP) measure. Recent studies instead used decomposed scenarios in which respondents report their WTP for each individual effect. Evidence can be found that the sum of such decomposed WTPs overestimates the holistic WTP, i.e. the holistic WTP is sub-additive. This sum of decomposed WTPs can lead to wrong conclusions on the efficiency of health technologies. This is also relevant in decision making about new technologies that are valued separately in different surveys. To date, no utility-theoretical and empirically validated aggregation function for decomposed WTPs exists. Within an expected utility model, this paper identifies as a reason for sub-additivity - beside risk aversion with respect to wealth - a negative influence of better health on the marginal utility of wealth, i.e. marginal utility of wealth is smaller in better health states. Assuming mutual utility independence of health and wealth, a theoretically founded aggregation function covering these two impacts is derived. In a contingent valuation study, 92 patients with diabetes were asked to state their WTP for reductions of the risk of several diabetic complications in decomposed as well as in holistic scenarios. The patients had preferences with a significant negative influence of health on the marginal utility of wealth. Sub-additivity occurred and theoretically founded aggregation could considerably lower the degree of overestimation. These results suggest that the theoretically founded aggregation function might reduce problems of sub-additivity that can be economically relevant. Further empirical testing of the approach is indicated.}, language = {en} }