__Abstract__ Health care expenditures have increased rapidly over the last decades in the Netherlands, in absolute terms and as percentage of gross domestic product. Curbing the rising health care costs has proven to be a very sensitive and complex societal issue. An important driver of rising costs is the availability and use of new and expensive medical technologies, causing a greater number of patients to be treated with more expensive interventions. Typically, these interventions do not only increase expenditures but also contribute to societal health and well-being. Since health care expenditures are high on the political agenda, policy makers are interested in the relative effectiveness and efficiency of new medical interventions: do they achieve larger health effects than other treatments, and if so, at what additional costs? Economic evaluations address this question. In economic evaluations, costs and effects of alternative medical interventions are compared, to see whether the new intervention offers good ‘value for money’. Researchers that which to apply economic evaluations to health care interventions face several methodological challenges. This thesis deals with one particular challenge: the measurement of the benefit of health care interventions in terms of quality of life.