Statistical analysis of quality of life data in cancer clinical trials

In clinical trials endpoints other than total and/or disease-free survival are gaining more and more interest. In particular, quality of life (QOL) or the well-being of patients has emerged as a synonym for variables describing the subjective reactions of patients towards their disease and its treatment. The statistical analysis of such QOL data is complicated firstly by the large number of variables measured and their obvious lack of objectivity. The construction of suitable aggregate measures allowing a reduction of the measurements into a (preferably) unidimensional index are discussed in the context of an analysis at a fixed time point during the course of treatment. A second problem arises from the consideration that a patient's well-being is subject to changes over time. We discuss the modelling of QOL by suitable stochastic processes which are extensions of a multistate disease process. This allows QOL events to be incorporated into methods of survival analysis by either estimating the relevant transition probabilities between states or calculating quality-adjusted survival times. Finally, some brief guidelines for the planning of clinical trials including QOL measurements will be proposed.