Linking physical function outcomes in rheumatology: performance of a crosswalk for converting Health Assessment Questionnaire scores to Short Form 36 physical functioning scale scores.
OBJECTIVE
To evaluate the reliability of a crosswalk, developed in The Netherlands, between the Health Assessment Questionnaire (HAQ) disability index (DI) and the Short Form 36 physical functioning scale (PF-10) in a sample of patients with various rheumatic diseases in the US.


METHODS
Baseline data from patients with rheumatoid arthritis (RA; n = 29,020), fibromyalgia (FM; n = 3,776), and systemic lupus erythematosus (SLE; n = 1,609) participating in the National Data Bank for Rheumatic Diseases were analyzed. Reliability of the crosswalk was evaluated by calculating intraclass correlation coefficients (ICCs), and agreement between observed and predicted scores was evaluated using the Bland-Altman approach. RESULTS. The crosswalk produced reliable conversions for both the HAQ DI (ICC range 0.70-0.77) and PF-10 (ICC range 0.73-0.78) in all 3 disease groups. The mean difference between observed and expected scores was close to zero in US patients with RA. For all 3 disease groups, the limits of agreement were fairly wide and conversion at the level of individual patients is not recommended.


CONCLUSIONS
The crosswalk produced reliable conversions at the group level in a crosscultural setting and can be used to convert HAQ DI to PF-10 scores and vice versa in US patients with RA, FM, or SLE.
Martijn A H
MA
Oude Voshaar
Peter M
PM
Ten Klooster
Erik
E
Taal
Frederick
F
Wolfe
Harald
H
Vonkeman
Cees A W
CA
Glas
Mart A F J
MA
Van De Laar
D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000175:diagnosis / Q000503:physiopathology; D015331:Cohort Studies; D003431:Cross-Cultural Comparison; D004185:Disability Evaluation; D005260:Female; D005356:Fibromyalgia / Q000175:diagnosis / Q000503:physiopathology; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000175:diagnosis / Q000503:physiopathology; D008297:Male; D008433:Mathematics / Q000379:methods*; D008875:Middle Aged; D009426:Netherlands; D063868:Patient Outcome Assessment; D015203:Reproducibility of Results; D012216:Rheumatic Diseases / Q000175:diagnosis* / Q000503:physiopathology*; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D014481:United States