Functional assessment in rehabilitative medicine: principles and methods.

In rehabilitative medicine, functional assessment means a decision process that results from the interaction between classifications (for example, diagnostic) and measures, and that aims to recognize, anticipate or modify the interaction between the disabled person and his environment. In this context, the measure is the intersection of a person along the conceptual gradient and continuum ''from less to more'' attributed to variability in the ''total person,'' such as independence, pain, cognitive capacity, or fatigability. The principal instrument is the additive questionnaire (functional scale). This consists of various items believed to represent a common variable. These kinds of variables are observable only partially across various aspects of the whole person, and are not completely predictable. Their measure, consequently, can only be derived from an estimated statistic. The additive questionnaire is the principal measurement instrument. Several items all representing the same variable receive scores whose sum is assumed to be proportional to the quantity of the underlying variable. For various reasons the sum of the scores does not represent a true linear and continuous measure like those seen in chemistry and physics. Recently developed methods, in particular Rasch analysis, can extract true measures from raw scores. Thanks to better measurement of variability in persons within rehabilitative medicine, functional assessment can become increasingly more valid and informative.