Item response theory methods can improve the measurement of physical function by combining the modified health assessment questionnaire and the SF-36 physical function scale.
OBJECTIVE
To compare the measurement properties of the Modified Health Assessment Questionnaire [MHAQ], the SF-36((R)) Health Survey 10 item Physical Functioning scale [PF10], and scores from an item response theory (IRT) based scale combining the two measures.


METHODS
Rheumatoid arthritis (RA) patients (n = 339) enrolled in a multi-center, randomized, double-blind, placebo-controlled trial completed the MHAQ and the SF-36 pre- and post-treatment. Psychometric analyses used confirmatory factor analysis and IRT models. Analyses of variance were used to assess sensitivity to changes in disease severity (defined by the American College of Rheumatism (ACR)) using change scores in MHAQ, PF10, and IRT scales. Analyses of covariance were used to assess treatment responsiveness.


RESULTS
For the entire score range, the 95% confidence interval around individual patient scores was smaller for the combined (total) IRT based scale than for other measures. The MHAQ and PF10 were about 70% and 50% as efficient as the total IRT score of physical functioning in discriminating among ACR groups, respectively. The MHAQ and PF10 were also less efficient than the total IRT score in discriminating among treatment groups.


CONCLUSIONS
Combining scales from the two short forms yields a more powerful tool with greater sensitivity to treatment response.
Martin
Marie
M
QualityMetric Incorporated, 640 George Washington Highway, Suite 201, Lincoln, 02865, RI, USA.
Kosinski
Mark
M
Bjorner
Jakob B
JB
Ware
John E
JE
Maclean
Ross
R
Li
Tracy
T
D000069594:Abatacept; D000203:Activities of Daily Living; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018501:Antirheumatic Agents / Q000627:therapeutic use; D001172:Arthritis, Rheumatoid / Q000188:drug therapy / Q000503:physiopathology* / Q000523:psychology; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D018796:Immunoconjugates / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D011594:Psychometrics / Q000295:instrumentation*; D011788:Quality of Life; D018434:Sickness Impact Profile; D011795:Surveys and Questionnaires
D018501:Antirheumatic Agents; D018796:Immunoconjugates; D000069594:Abatacept