International Classification of Functioning, Disability, and Health

ICF's Conceptual Model

The underlying rationale of the ICF is that the lived experience of health is primarily a matter of the range and extent of functioning across all domains. Classifying human functioning requires a distinction between functioning at the body level (e.g., visual acuity, digestive functions, metabolic functions, and muscle functions) and the level of the whole person (thinking, communicating, walking, maintaining interpersonal relationships, attending school, and working). These functions, simple and complex, identify basic bodily functions and human capacities to perform actions and display behaviors that constitute a person's state of health. A third level of functioning completes the picture of the lived experience of health by characterizing functioning as an outcome of the interaction between body and person level capacities and the complete physical, human-built, social, and attitudinal environment. ICF is therefore a classification of the full range of human functioning and decrements in function—that is, disabilities—at the body and person levels, as well as the actual performance of these capacities, within and as modified by the complete context of the individual's world (Figure 1).

The concept of ‘disability’ in the ICF therefore refers to decrements or difficulties encountered in functioning at all three levels of functioning. Decrements in body functions are called impairments, [Page 552]decrements in person level capacities are called activity limitations, and difficulties in performing in context all human actions and displaying behaviors constitutive of the lived experience of health are called participation restrictions. Impairments and activity limitations are fully within the domain of health (indeed a fully operationalizable definition of health for measurement purposes can be given in terms of functions), whereas participation restrictions, as outcomes of person-environment interactions, are outside the domain of health, although associated directly with health states.

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