The significance of contextual factors in valuing health states.
QALY analysis consists of describing the effects of a programme in terms of a stream in a patient-time field after which the stream is evaluated. The stream concept represents a considerable advance compared to for instance describing the outcome of health care in terms of survival rates. The valuation task, on the other hand, poses difficult problems. Several contextual factors may significantly affect the social value assigned to a health improvement in a particular patient-year. None of these factors is included in the current algorithm for calculating social utility in terms of QALYs. The factors are set together in a model that may serve as a framework within which QALY calculations may be considered. Examples are given of how QALY calculations can be misleading if these factors are not taken into account.