A Health-Status Index and its Application to Health-Services Outcomes

In order to develop an operational definition of health, we found it necessary first to develop the concept of function/dysfunction as a continuum, based on one's ability to carry on the usual daily activities appropriate to social roles. Then, to those operating the health system, each member of the population can be seen as belonging to one and only one state from a class of functional states that can be defined on an ordinal scale. Next, we found it necessary to assign to each state a weight defined on a cardinal scale, the set of weights for these states being called the Health Status Index (HSI). The HSI rests on value judgments, of a societal nature, expressed by the administrators responsible for policy decisions. Prognosis is then defined as the transitional probability of a change in functional state with time. Thus, the concepts “state of health” and “severity of illness” are decomposed into the parameters function/dysfunction and prognosis. Finally, together with an operational definition of time and target population, it becomes possible to give a quantitative definition of the output of a health program (or health system) as the changes in the functional history of the target population resulting from the intervention of the health program (or system). Other concepts that are given quantitative definitions are program effectiveness and population health status. This study next explores the relation between health program output and modern decision theory for program planning, and shows how these analytical tools are useful for fitting the results of the study into larger conceptual frameworks. Finally, the method developed is illustrated, first with a simplified simulated program for computer use, and then with an analysis of a small section of a tuberculosis-control program.