English Banner 

Concepts and Definitions of Disability   Return to Disability Theme page

1. Core Knowledge:

The contemporary conception of disability proposed in the WHO International Classification of Functioning, Disability and Health (ICF) views disability as an umbrella term for impairments, activity limitations and participation restrictions. Disability is the interaction between individuals who have a health condition (e.g. cerebral palsy, Down syndrome or depression) and personal and environmental factors (e.g. negative attitudes, inaccessible transportation, or limited social supports).

Long ago there was great confusion over the meaning of terms such as impairment, handicap, or disability.  Then, in 1980, the WHO provided great service by offering a clear way of thinking about it all in a little book called "International Classification of Impairments, Disabilities and Handicaps".

All these terms refer to different levels of consequences of disease.  The disease produces some form of pathology, and then the individual may become aware of this: they experience symptoms.  Later, their performance or behaviour may be affected, and because of this they may suffer consequences such as being unable to work.  In this general scenario, 

Impairment was defined as "any loss or abnormality of psychological, physiological, or anatomical structure or function."  Impairment is a deviation from normal organ function; it may be visible or invisible (screening tests generally seek to identify impairments).

Disability was defined as "any restriction or lack (resulting from an impairment) of ability to perform an activity in the manner or within the range considered normal for a human being."  An impairment does not necessarily lead to a disability, for the impairment may be corrected.  I am, for example, wearing eye glasses, but do not perceive that any disability arises from my impaired vision.  A disability refers to the function of the individual (rather than of an organ, as with impairment).

In turn, Handicap was defined as "a disadvantage for a given individual, resulting from an impairment or a disability, that limits or prevents the fulfillment of a role that is normal (depending on age, sex, and social and cultural factors) for that individual."  Handicap considers the person's participation in their social context.  For example, if there is a wheel-chair access ramp at work, a disabled person may not be handicapped in coming to work there. 

Here are some examples:
Impairment - Speech production; Disability - Speaking clearly enough to be understood; Handicap - Communication
I - Hearing; D - Understanding; H - Communication
I - Vision; D - Seeing; H - Orientation
I - Motor control, balance, joint stiffness; D - Dressing, feeding, walking; H - Independence, mobility
I - Affective, cognitive limitations; D - Behaving, interacting, supporting; H - Social interaction, reasonableness

This diagram suggests possible parallels between the impairment, disability & handicap triad, and the disease, illness and sickness triad. (The squiggly arrows are intended to indicate a rough correspondence)

The links between natural history of a disease and the categories of disability

"Patients do not come to their physicians to find out what ICD code they have, they come to get help for what is bothering them."


2. Nice to Know:

A Positive Perspective?  Quality of Life and the International Classification of Function
The conventional focus on disability takes a somewhat negative approach to health, perhaps not unreasonable since doctors are supposed to cure diseases. But some people have pointed out that the medical model of disability is grounded in the perspective that “disability resides in the individual and carries with it a degree of stigma or pathology.” In contrast, the social model places the locus of disability in the environment that fails to appropriately accommodate and include people with disabilities. A point worth pondering, perhaps!

Starting in the 1980s clinicians began to tackle the challenge of how to describe the goals of medicine when the disease could not be cured, beyond merely controlling symptoms. The notion of Quality of Life gained prominence as a way to emphasize a positive perspective on health - enhancing a person's capacity to function and to live, even if the person has an incurable condition. A central aim of care was to enhance the quality of the patient's function, and hence their ability to life as normal a life as possible, even if the disorder could not be cured. Quality of life was a further extension of handicap, covering maintenance of normal function, but adding psychological well-being, plus positive feelings of engagement, purpose in life and the ability to enjoy the possibilities that their life brings. Quality of life is an inherently subjective concept, judged by the person themselves.

Measurements of quality of life extend the disability focus beyond the ability to perform activities of daily living to include a broad range of functioning (work, home, play) and also the person's feelings of satisfaction and well-being. This is a qualitative concept, judged by the patient in terms of the extent to which they are able to do the things they wish to do. In the medical context, we refer to "Health-related quality of life" which is distinct from wealth or possessions, which form aspects of material quality of life that are not consideredand relevant as outcomes of care.

Reflecting these evolving ideas, the WHO revised its Impairment, Disability and Handicap triad in 2001, re-naming it the International Classification of Function (ICF). This classification system provides codes for the complete range of functional states; codes cover body structures and functions, impairments, activities and participation in society. The ICF also considers contextual factors that may influence activity levels, so function is viewed as an interaction between health conditions (a disease or injury) and the context in which the person lives (both physical environment and cultural norms relevant to the disease). It establishes a common language for describing functional states that can be used in comparing across diseases and countries. The ICF therefore uses positive language, so that "activity" and "participation" replace "disability" and "handicap." The ICF is described on the WHO web site.


“Disability is not contagious but your attitude might be”



Updated January 30, 2015