Objective To develop and validate a parent-centered and a child-centered composite disease assessment index for juvenile idiopathic arthritis (JIA): the Juvenile Arthritis Parent Assessment Index (JAPAI) and the Juvenile Arthritis Child Assessment Index (JACAI), respectively. Methods The JAPAI and the JACAI include 4 measures: parent/child rating of overall well-being, pain, physical function, and health-related quality of life (HRQOL). Validation analyses were conducted on nearly 5,000 patients and included assessment of construct validity, discriminant validity, responsiveness to change, and reliability. Besides the 4-item version, a 3-item version of both indices, which did not include HRQOL, was tested. Results The JAPAI and the JACAI demonstrated good construct validity, yielding high correlations with the Juvenile Arthritis Disease Activity Score and moderate correlations with physician global rating and joint counts. Correlations obtained for the JAPAI and the JACAI and for the 4-item and the 3-item versions were comparable. Factorial analysis by principal component analysis showed that both indices are monodimensional. Both the JAPAI and JACAI discriminated well between different disease states and courses and between different levels of American College of Rheumatology Pediatric criteria in a clinical trial, and revealed fair responsiveness to clinical change. Internal consistency was satisfactory, with a Cronbach's alpha of >0.80 in all but 1 of the patient samples tested. Conclusion The JAPAI and the JACAI were found to be valid instruments for assessment of disease status in JIA and suitable surrogates of physicians' evaluations. Both indices are potentially applicable in clinical practice, observational studies, and therapeutic trials.
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