Quality of life and social production functions: a framework for understanding health effects.

Quality of life (QofL) has emerged as a new outcome paradigm. It is now the endpoint in various taxonomies of patient outcomes, in which relationships are modeled amongst biological abnormalities, symptom status, functional status, disability, health perceptions and quality of life. Although current models and taxonomies point at important determinants of QofL, they do not provide a heuristic that guides the conceptualization of QofL and the systematic development of an explanatory theory of how ill health affects QofL. General mechanisms linking ill health, behavior, and QofL are lacking. In this paper we propose social production function (SPF) theory as providing such a heuristic, relating the effects of ill health, the activities that patients engage in to maintain QofL, and QofL itself. This theory basically asserts that people produce their own well-being by trying to optimize achievement of universal human goals via six instrumental goals within the environmental and functional limitations they are facing. Three important notions of SPF theory are: (1) the linkages between goals, needs, and well-being; (2) the distinction between universal needs and instrumental goals; and (3) substitution among instrumental goals, activities and endowments according to cost-benefit considerations, whereby costs refer to scarce resources such as functional capacity, time, effort and money. We will argue that SPF theory meaningfully relates the "biomedical model"-with its focus on pathological processes and biological, physiological and clinical outcomes-to the "quality of life" model, with its focus on functioning and well-being. We describe SPF theory and how SPF theory can be used to: (1) operationally define and measure QofL; (2) clarify persistent measurement problems; and (3) develop an explanatory framework of the effects of disease on QofL. In the discussion section, we address the limitations of the SPF approach of QofL and its relationship with personality.