['To provide evidence of construct validity for the FIM instrument in the inpatient rehabilitation burn population.', "Confirmatory factor analysis and item response theory were used to assess construct validity. Confirmatory factor analysis was performed on a 2-factor model of the FIM instrument and on a 6-subfactor model. Mokken scale analysis, a nonparametric item response theory, was performed on each of the FIM instrument's 2 major factors, motor and cognitive domains. Internal consistency using Cronbach alpha and Molenaar and Sijtsma's statistic was also examined.", 'Inpatient rehabilitation facilities.', 'Data from the Uniform Data System for Medical Rehabilitation for patients with an impairment code of burn injury from the years 2002 to 2011 were used for this analysis. A total of 7569 subjects were included in the study.', 'Not applicable.', 'Comparative fit index results for the confirmatory factor analyses and adherence to assumptions of the Mokken scale model.', 'Confirmatory factor analysis provided a comparative fit index of .862 for the 2-factor model and .941 for the 6-subfactor model. Mokken scale analysis showed scalability coefficients of .681 and .891 for the motor and cognitive domains, respectively. Measures of internal consistency statistic gave values of >.95 for each major domain of the FIM instrument.'] Do validity and reliability of the FIM instrument in the inpatient burn rehabilitation population?