Cross-cultural validity of Functional Independence Measure items in stroke: A study using Rasch analysis

Objective: To analyse cross-cultural validity of the Functional Independence Measure (FIM™) in patients with stroke using the Rasch model. Settings: Thirty-one rehabilitation facilities within 6 different countries in Europe. Participants: A total of 2546 in-patients at admission, median age 63 years. Methods: Data from the FIM™ were evaluated with the Rasch model, using the Rasch analysis package RUMM2020. A detailed analysis of scoring functions of the 7 categories of the FIM items was undertaken prior to testing fit to the model. Categories were re-scored where necessary. Analysis of Differential Item Functioning was undertaken in pooled data for each of the FIM motor and social-cognitive scales, respectively. Results: Disordered thresholds were found on most items when using 7 categories. Fit to the Rasch model varied between countries. Differential Item Functioning was found by country for most items. Adequate fit to the Rasch model was achieved when items were treated as unique for each country and after a few country-specific items were removed. Conclusion: Clinical collected data from FIM for patients with stroke cannot be pooled in its raw form, or compared across countries. Comparisons can be made after adjusting for country-specific Differential Item Functioning, though the adjustments for Differential Item Functioning and rating scales may not generalize to other samples.