A reformulation of quality of life for medical science.

Current quality of life measuring tools are suited for economic decision making, not to investigate causal processes which lead to patients making evaluations of their lives. An alternative approach is presented based on research into positive versus negative life-satisfaction. Quality of life is a causal sequence of psychological states where perceived symptoms cause problems and the problems and symptoms cause evaluations, and where the causal sequence is a complex interaction between morbidity and psychological factors. Different types of medical intervention affect different stages in the causal sequence and so different types of quality of life instrument are needed for different kinds of medical research.