What is the difference between impairment and disability?

Impairment
According to the fifth edition of the Guides to the Evaluation of Permanent Impairment, published by the American Medical Association (AMA), impairment is defined as "an alteration of an individual's health status; a deviation from normal in a body part or organ system and its functioning."1,2,3 The World Health Organization (WHO) defines impairment as "any loss or abnormality of psychological, physiological or anatomical structure or function."4



The Social Security Administration (SSA) defines a medically determinable impairment as "an impairment that results from anatomical, physiological, or psychological abnormalities which can be shown by medically acceptable clinical and laboratory diagnostic techniques."5,6,7,8 The SSA further states that a physical or mental impairment "must be established by medical evidence consisting of signs, symptoms, and laboratory findings—not only by the individual's statement of symptoms."

According to the AMA Guides, impairments that are to be rated are permanent impairments. A permanent impairment is defined as one that has reached maximum medical improvement (MMI) and is well stabilized and unlikely to change substantially in the next year with or without medical treatment. Each state workers' compensation system has its own definition of impairment. These definitions may vary from state to state but are generally consistent with the definition expressed in the AMA Guides.9

Disability

According to the fifth edition of the AMA Guides, disability is defined as "an alteration of an individual's capacity to meet personal, social, or occupational demands because of an impairment."2,10 The WHO defines disability as an activity limitation that creates a difficulty in the performance, accomplishment, or completion of an activity in the manner or within the range considered normal for a human being. Difficulty encompasses all of the ways in which the performance of the activity may be affected.

On the other hand, the SSA defines disability as "the inability to engage in any substantial, gainful activity by reason of any medically determinable physical or mental impairment(s), which can be expected to result in death or which has lasted or can be expected to last for a continuous period of not less than 12 months."5,6,7,8 Workers' compensation systems usually define disability as a reduction in wage-earning capacity as a result of an injury, illness, or occupational disease that arose out of, or in the course of, employment.
Distinguishing the difference between impairment and disability is imperative. One individual can be impaired significantly and have no disability, while another person can be quite disabled with only limited impairment. For example, a person with paraplegia who is wheelchair-bound may be working full time quite successfully as an accountant and, therefore, would not meet the SSA's definition of disability. On the other hand, a concert pianist might have a relatively minor injury to a digital nerve that severely limits his/her ability to perform basic work activities (playing difficult piano concertos). In some disability systems, a person in this situation might meet the definition of disabled even though he/she can do other work.
Because of this difference between impairment and disability, physicians are encouraged to rate impairment based on the level of impact that the condition has on the performance of activities of daily living (ADL) rather than on the performance of work-related tasks.11 According to the AMA Guides, impairment ratings derived from the AMA Guides are "not intended for use as direct determinants of work disability."
Interestingly, various professionals and institutions regularly use the AMA Guides for the direct measurement of disability. Most states recognize the impairment ratings determined by the AMA Guides as direct measures of disability, despite the stated intent of the authors.
Disability can be temporary or permanent, and it can be partial or total.12,13 Various programs have various categories of disability. An individual can be temporarily unable to perform work activity for remuneration or profit (for example, after trauma, surgery, and/or intensive care) and can be classified as disabled under some disability programs. However, if recovery occurs within 12 months, the individual is not likely to be classified as disabled under the SSA's permanent disability program.

Many workers' compensation systems allow for partial disability, generating a need for the AMA Guides to measure the extent of the impairment as related to normal functional capacity.12,13,14 The SSA disability program, on the other hand, is an all-or-nothing type of program; the claimant is considered either entirely disabled or not disabled. The Americans with Disabilities Act (ADA) confuses the definition of disability even further. According to the act, disability is present if at least 1 of the following requirements has been fulfilled:
A physical or mental impairment that substantially limits at least 1 of an individual's major life activities
A record of such an impairment
Being regarded as possessing this sort of an impairment
With this broad definition of what constitutes a disability, virtually everyone with a health problem could argue that they have a disability. Further complicating the ADA definition—as ADA cases are tried in the courts—is the ever-changing legal definition of disability.
Defining impairment and disability is not an easy task, as can be seen by the differences in the above-cited perceptions. The definition of these terms varies depending on the circumstances involved in a specific case. This article provides insight into the varying interpretations, definitions, and applications of the concept of disability.