A multicenter international study on the Spinal Cord Independence Measure, version III:: Rasch psychometric validation

Background: A third version of the Spinal Cord Independence Measure ( SCIM III), made up of three subscales, was formulated following comments by experts from several countries and Rasch analysis performed on the previous version. Objective: To examine the validity, reliability, and usefulness of SCIM III using Rasch analysis. Design: Multicenter cohort study. Setting: Thirteen spinal cord units in six countries from North America, Europe, and the Middle-East. Subjects: 425 patients with spinal cord lesions ( SCL). Interventions: SCIM III assessments by professional staff members. Rasch analysis of admission scores. Main outcome measures: SCIM III subscale match between the distribution of item difficulty grades and the patient ability measurements; reliability of patient ability measures; fit of data to Rasch model requirements; unidimensionality of each subscale; hierarchical ordering of categories within items; differential item functioning across classes of patients and across countries. Results: Results supported the compatibility of the SCIM subscales with the stringent Rasch requirements. Average infit mean-square indices were 0.79-1.06; statistically distinct strata of abilities were 3 to 4; most thresholds between adjacent categories were properly ordered; item hierarchy was stable across most of the clinical subgroups and across countries. In a few items, however, misfit or category threshold disordering were found. Conclusions: The scores of each SCIM III subscale appear as a reliable and useful quantitative representation of a specific construct of independence after SCL. This justifies the use of SCIM in clinical research, including cross-cultural trials. The results also suggest that there is merit in further re. ning the scale.