Discrete or Continuous Phenomena

Disability is commonly presented as an all or nothing phenomenon, either a person “is disabled or not.” In reality, disability in particular roles or activities is usually encountered in terms of degree of difficulty, limitation, or dependence, ranging from slight to severe. The question then becomes: Where on the disability spectrum is the threshold that determines whether a person has a disability or work disability? The question needs to take into account any assistive devices or accommodations that the person may have. In the current context, work participation is often determined as being an end point, in that people either have a work disability or they do not. In reality, the situation is likely to be more complex. For example, many people with functional and activity limitations may continue to work, but their labor force participation may be compromised in some way by the condition, including the opportunity to work. To the extent that it is, these people might be said to have some degree of work disability. In measuring work disability, a clear definition of the threshold used needs to be made.

Duration or Chronicity

There is a pervasive assumption that work disability is a long-term state. Stereotypes about disability are dominated by the archetype of a person who uses a wheelchair. Embedded in this is the notion of some disabling event, a period of adjustment and rehabilitation, and then the resumption of as full a life as possible with the assistance of any necessary assistive devices or accommodations. With much impairment, the reality of disability is somewhat different. The majority of individuals in the working age population with long-term activity restriction report that this restriction is due to musculoskeletal, circulatory, or respiratory disorders (LaPlante et al., 1996). These conditions may also be associated with varying degrees of “illness,” so that it is not just an issue of physical performance. Other considerations are pain, fatigue, and other symptoms. Many of these conditions are episodic in nature and may have trajectories of either deterioration or recovery (the latter being less common). Apart from any environment barriers or facilitators, the day-to-day or month-to-month experience of disability may be variable and may need to be taken into account in any measurement scheme.

In summary, researchers have attempted to define disability by designing models (or paradigms) that document the process of becoming disabled. While each of these models suggests a theoretical definition of disability, none offers a detailed operational definition. All definitions agree, however, in viewing disability as an intersection between the indi-



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