Dr. Gale Whiteneck began with a brief history of models of disability. (The paper prepared by Dr. Whiteneck appears in Appendix B.) He noted in particular the seminal contribution of Saad Nagi in differentiating disability-related outcomes at three levels, namely, the organ, the person, and society. Dr. Whiteneck then focused on an assessment of the transition from the International Classification of Impairments, Disabilities and Handicaps (ICIDH) to the International Classification of Functioning, Disability and Health (ICF), which were published by the World Health Organization (WHO) in 1980 and 2001, respectively (WHO, 1980, 2001). ICF and its associated description offered one major conceptual step forward but also one step backward. Drawing on his experience with the classification revision process, Dr. Whiteneck proposed that several additional steps are needed to revise and apply the model.

The major step forward with ICF was the inclusion of physical, social, and other environmental factors that interact with an individual’s health conditions and other characteristics to produce outcomes, including activity (defined as the execution of a task or action by an individual) and participation (defined as an individual’s involvement in a life situation). This step was consistent with the recommendations of the IOM committees in 1991 and 1997 (IOM, 1991, 1997) and also with the provisions of the Americans with Disabilities Act (ADA; P.L. 101-336), which became law in 1990.

Other improvements in the classification involved the incorporation of neutral as well as negative ways of describing an individual’s status. For example, the ICF model uses the neutral phrase “body function and structure” as well as the term “impairment” and includes the term “activity” as well as “activity limitation.” The revised model also emphasized the complexity of possible interactions among its components (e.g., as shown by the two-way arrows rather than one-way “causal” arrows in the model’s graphic representation).

The step backward with ICF was the blurring of the conceptual distinctions between activity and participation (and between activity limitations and participation restrictions). Rather than identifying certain difficulties as activity limitations and other difficulties as participation restrictions, ICF grouped them together in a single list. Among the many differences between the two concepts, the foremost is that activity (e.g., walking) operates primarily at the person level, whereas participation (e.g., working) operates at the social and societal level. Activities are generally simpler than participation, and participation is more dependent on environmental factors than