Disability Epidemiology

The practice of disability epidemiology includes consideration of the basic elements of descriptive epidemiology (who, what, where), etiological determinants of impairments, and the frequency and predictors of different outcomes of disability. All these questions incorporate the common epidemiology study designs and methods. Adapting from John Last's classic definition of epidemiology, disability epidemiology is, then, the study of the distribution, determinants, correlates, and outcomes of disability and application of this study to maximizing the health and quality of life of people and populations with disability (PWD).

The concepts and content of disability epidemiology derive naturally from a number of other epidemiology disciplines, such as injury, neurological diseases, maternal and child health, aging, and outcomes research. Despite some differences in methods and focus, epidemiology principles do not alter remarkably as one moves from one content area to another.

However, unlike specific disease areas (e.g., neurological diseases), the focus of disability epidemiology is less concerned with diagnoses and specific impairments than with broad functional levels, such as mental, sensory, and mobility. This focus is derived from the definition of disability found in the World Health Organization (WHO) International Classification of Functioning, Health and Disability (ICF), which is based on a social versus a traditional medical model of disability. This paradigm moves from a diagnosis and treatment model of disability to one where people are defined in the broader context of social roles and participation—so that consideration of disability is essentially removed from the constraints of medical care and definitions. In this paradigm, disability is an umbrella term, where participation (the key outcome) is a function of aspects of environment, intrinsic personal factors, body function and structure, and activities. The ICF has been proposed as the unifying framework for disability measurement in public health.

In the ICF paradigm, disability must be defined as a state that is largely independent of health and health status. The distinction between the two is difficult to incorporate into traditional epidemiology, however. While epidemiologists are comfortable with the notion of prevention occurring at primary, secondary, and tertiary levels, in disability research, prevention includes both prevention of new primary disabilities or impairments and prevention of the adverse outcomes of disability. This separation of health and disability is accomplished in the Healthy People 2010 chapter on disability. Prominent in this document is the following basic assumption about disability: