Several models that depict the process of disablement have been proposed over the past 40 years. The first two schema developed were the Nagi model and the International Classification of Impairments, Disabilities, and Handicaps (ICIDH) model for the World Health Organization (WHO). The ICIDH model was revised after its original publication, with adjustments made in the descriptions of the classification criteria of the model based on input from health-care practitioners as they became familiar with the original model.

The National Center for Medical Rehabilitation Research (NCMRR) integrated components of the Nagi model with the original ICIDH model to develop its own model. The NCMRR model added interactions of individual risk factors, including physical and social factors, to the disablement process.

Although each of these models uses slightly different terminology, each reflects a spectrum of disablement. Several sources in the literature have discussed or compared and contrasted the terminology and descriptors used in these and other models. Despite the variations in these models, each taxonomy reflects the complex interrelationships among the following.

• Acute or chronic pathology
• Impairments
• Functional limitations
• Disabilities, handicaps, or societal limitations

The conceptual frameworks of the Nagi, ICIDH, and NCMRR models of disablement, although applied widely in clinical practice and research in many health-care professions, have been criticized for their perceived focus on disease and a medical-biological view of disability as well as their lack of attention to the person with a disability. In response to these criticisms, the WHO undertook a broad revision of its conceptual framework and system for classifying disability described in its ICIDH model. Through a comprehensive consensus process over a number of years, the WHO developed the International Classification of Functioning, Disability, and Health (ICF). This new conceptual model integrates functioning and disability and is characterized as a bio-psycho-social model of disablement that provides a coherent perspective of various aspects of health. The revised model was also designed to place less emphasis on disease and greater emphasis on how people affected by health conditions live.

The ICF model consists of the following components of health and health-related influences.

• Impairment of body structure (anatomical) and function (physiological)
• Activity limitation
• Participation restriction
• Impact of contextual factors (environmental and personal) on functioning, disability, and health

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