Assessing and adjusting for cross-cultural validity of impairment and activity limitation scales through differential item functioning within the framework of the Rasch model: the PRO-ESOR project.
BACKGROUND
In Europe it is common for outcome measures to be translated for use in other languages. This adaptation may be complicated by culturally specific approaches to certain tasks; for example, bathing. In this context the issue of cross-cultural validity becomes paramount.


OBJECTIVE
To facilitate the pooling of data in international studies, a project set out to evaluate the cross-cultural validity of impairment and activity limitation measures used in rehabilitation from the perspective of the Rasch measurement model.


METHODS
Cross-cultural validity is assessed through an analysis of Differential Item Functioning (DIF) within the context of additive conjoint measurement expressed through the Rasch model. Data from patients undergoing rehabilitation for stroke was provided from 62 centers across Europe. Two commonly used outcome measures, the Mini-Mental State Examination (MMSE) and the Functional Independence Measure (FIM) motor scale are used to illustrate the approach.


RESULTS
Pooled data from 3 countries for the MMSE were shown to fit the Rasch model with only 1 item displaying DIF by country. In contrast, many items from the FIM expressed DIF and misfit to the model. Consequently they were allowed to be unique across countries, so resolving the lack of fit to the model.


CONCLUSIONS
Where data are to be pooled for international studies, analysis of DIF by culture is essential. Where DIF is observed, adjustments can be made to allow for cultural differences in outcome measurement.
Tennant
Alan
A
Academic Unit of Musculoskeletal and Rehabilitation Medicine, University of Leeds, 36 Clarendon Road, Leeds, LS2 9NZ, United Kingdom. a.tennant@leeds.ac.uk
Penta
Massimo
M
Tesio
Luigi
L
Grimby
Gunnar
G
Thonnard
Jean-Louis
JL
Slade
Anita
A
Lawton
Gemma
G
Simone
Anna
A
Carter
Jane
J
Lundgren-Nilsson
Asa
A
Tripolski
Maria
M
Ring
Haim
H
Biering-Sørensen
Fin
F
Marincek
Crt
C
Burger
Helena
H
Phillips
Suzanne
S
D000203:Activities of Daily Living / Q000145:classification* / Q000523:psychology; D000223:Adaptation, Psychological; D000704:Analysis of Variance; D003431:Cross-Cultural Comparison; D004185:Disability Evaluation; D005060:Europe; D005260:Female; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D017063:Outcome Assessment, Health Care / Q000379:methods* / Q000706:statistics & numerical data; D025341:Principal Component Analysis; D011336:Probability; D011594:Psychometrics / Q000706:statistics & numerical data; D020127:Recovery of Function / Q000502:physiology; D015203:Reproducibility of Results; D020377:Self Efficacy; D012680:Sensitivity and Specificity; D018434:Sickness Impact Profile; D020521:Stroke / Q000523:psychology; D000071939:Stroke Rehabilitation; D011795:Surveys and Questionnaires / Q000592:standards