The demand-for-health model provides guidance for research in all these areas. There are, however, several aspects of health-related behaviour that need further theoretical and empirical attention. A more technical criticism of the demand-for-health model that has been mentioned in the literature concerns the fact that health is treated as endogenous to the degree that the individual in effect decides about his or her time of death. Empirical estimates of the demand-for-health model have not unambiguously agreed with the theoretical predictions derived from the model.