Health and the life course are two broad concepts of interest to sociologists. Each of these concepts must be nominally defined.

Conceptions of Health

Health can be conceptualized in three major ways: the medical model (or physical definition); the functional model (or social definition); and the psychological model (or the subjective evaluation of health: Liang 1986). In the medical model, health is defined as the absence of disease. The presence of any disease condition is determined by reports from the patient, observations by health practitioners, or medical tests. The social definition of health is derived from Parsons's (1951) work and refers to an individual's ability to perform roles, that is, to function socially. Illness or impairment is a function of reduced capacity to perform expected roles, commonly measured in terms of activities of daily living (ADLs—eating, dressing, bathing, walking, grooming, etc...