The Functional Independence Measure (FIM) of S. Forer and others (1987) records the degree of disability of rehabilitation patients between "Total Dependence" and "Complete Independence." Using the FIM, ratings on a seven-point scale are made by therapists and other expert care-providers at the time of patient admission to rehabilitation, at the time of patient discharge from rehabilitation, and at a follow-up assessment several weeks after patient discharge. The effectiveness of the rehabilitation program is measured by comparing the FIM scores for a patient at admission and at discharge. Rasch analysis of the admission or discharge FIM ratings of a sample of 33,646 patients shows that the 18 items of the FIM do not define a single statistical variable. Analysis highlights two statistically and substantively different variables: (1) disability in motor functions; and (2) disability in cognitive functions. Separate Rasch analysis of these two variables confirms this conclusion and suggests further refinements that would increase FIM usefulness. Three tables contain study data. The FIM is presented. (Author/SLD)