A comparison of the measurement properties of the Juvenile Arthritis Functional Assessment Scale with the childhood health assessment questionnaire in daily practice.

We compared the measurement properties of a performance test (Juvenile Arthritis Functional Assessment Scale; JAFAS) with a questionnaire-based instrument (Childhood Health Assessment Questionnaire; CHAQ) to measure functional ability in patients with juvenile idiopathic arthritis on the level of individual items. In 28 consecutive children visiting an outpatient paediatrics clinic, the JAFAS (range 0-20) and CHAQ (range 0-3) were applied, and measures of disease activity and joint range of motion (ROM) were determined. Twenty-eight children with a median age of 10 years and median disease duration of 3.2 years were included. The median JAFAS score was 0, and the median CHAQ score was 0.125. Cronbach's alpha was 0.92 for the JAFAS and 0.96 for the CHAQ. The Spearman correlation coefficient between the JAFAS and the CHAQ was 0.55 (P < 0.01). With six out of ten items, the JAFAS classified the child as less disabled than with corresponding CHAQ activities. Overall, associations with measures of disease activity and ROM were higher for the CHAQ than for the JAFAS. A performance test (JAFAS) does not appear to have an added benefit over the questionnaire-based assessment (CHAQ) of physical function in a cross-sectional study.