Cross-diagnostic validity in a generic instrument: an example from the Functional Independence Measure in Scandinavia
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Cross-diagnostic validity in a generic instrument: an example from the Functional Independence Measure in Scandinavia Å Lundgren-Nilsson*2, A Tennant1, G Grimby2 and KS Sunnerhagen2 Address: 1Department of Rehabilitation Medicine, Academic Unit of Musculoskeletal Disease, The University of Leeds, 36 Clarendon Road, Leeds, LS2 9NZ, UK and 2Sahlgrenska Academy at Göteborg University, Institute of Neuroscience and Physiology/Rehabilitation medicine, Guldhedsgatan 19 413 45 Göteborg, Sweden Email: Å Lundgren-Nilsson* - [email protected]; A Tennant - [email protected]; G Grimby - [email protected]; KS Sunnerhagen - [email protected] * Corresponding author
Published: 23 August 2006 Health and Quality of Life Outcomes 2006, 4:55
doi:10.1186/1477-7525-4-55
Received: 08 March 2006 Accepted: 23 August 2006
This article is available from: http://www.hqlo.com/content/4/1/55 © 2006 Å et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract Background: To analyse the cross-diagnostic validity of the Functional Independence Measure (FIM™) motor items in patients with spinal cord injury, stroke and traumatic brain injury and the comparability of summed scores between these diagnoses. Methods: Data from 471 patients on FIM™ motor items at admission (stroke 157, spinal cord injury 157 and traumatic brain injury 157), age range 11–90 years and 70 % male in nine rehabilitation facilities in Scandinavia, were fitted to the Rasch model. A detailed analysis of scoring functions of the seven categories of the FIM™ motor items was made prior to testing fit to the model. Categories were re-scored where necessary. Fit to the model was assessed initially within diagnosis and then in the pooled data. Analysis of Differential Item Functioning (DIF) was undertaken in the pooled data for the FIM™ motor scale. Comparability of sum scores between diagnoses was tested by Test Equating. Results: The present seven category scoring system for the FIM™ motor items was found to be invalid, necessitating extensive rescoring. Despite rescoring, the item-trait interaction fit statistic was significant and two individual items showed misfit to the model, Eating and Bladder management. DIF was also found for Spinal Cord Injury, compared with the other two diagnoses. After adjustment, it was possible to make appropriate comparisons of sum scores between the three diagnoses. Conclusion: The seven-category response function is a problem for the FIM™ instrument, and a reduction of responses might increase the validity of the instrument. Likewise, the removal of items that do not fit the underlying trait would improve the validity of the scale in these groups. Crossdiagnostic DIF is also a problem but for clinical use sum scores on group da
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