The primary aim of this study was to compare responsiveness of self-report by worker and therapist-scored functional capacity instrument. Self-report and therapist-scored interval-level person measures and item difficulties were compared at admission and discharge. Therapist and worker ratings were collected on 230 clients from 27 rehabilitation sites using the newly developed Occupational Rehabilitation Data Base (ORDB) functional capacity instrument. ORDB comprises several subscales measuring relevant variables of "a return-to-work model" in work-related rehabilitation clinics. The functional capacity scale deals with 10 DOT job factors. The rating scale categories were 1-severely impaired, 2-moderately impaired, 3-mildly impaired, and 4-not impaired. Only data from clients with low back pain (n=98) with complete data (both admission and discharge scores) were used for the present study. Therapists and workers completed the functional capacity instrument at admission and discharge. Rasch analysis [1-parameter item response theory model (IRT)] was applied to calibrate item difficulty and person ability measure of therapist and workers ratings. Effect sizes for therapist and self-report ratings were slightly different, .69 and .30, respectively. Therapist and worker ratings were more consistent at discharge (r=.54) than at admission (r=.32). Workers have a tendency to be more severe in their ratings (show higher item difficulties) than therapists at admission and discharge. Therapists and workers report similar magnitudes of improvement following treatment program. These findings challenge the belief that injured workers may unreliable source for monitoring therapeutic outcomes. Self-report measures have the advantage of conserving therapist time for treatment (versus evaluation). While the therapist and self-report ratings are comparable at discharge, there is less consistency at admission. Comparable therapist-worker ratings may be achieved by controlling for rating severity using IRT methodologies.