To determine whether the Childhood Health Assessment Questionnaire (CHAQ) is valid for the comparison of different age subgroups and for longitudinal studies in juvenile idiopathic arthritis (JIA).
A CHAQ was administered to 306 children with JIA. Rasch analyses were used to compare the difficulty of each of the 30 items of the questionnaire for children of 2 age groups (> or =10 years old and <10 years old).
Independent of the physical disability level assessed by the Rasch model, 8 of the 30 items (27%) of the CHAQ were rated significantly different in the 2 age groups. Despite this age-related variation in item difficulty, the impact on the CHAQ disability index using its original scoring system remained low (about 0.25 points on a scale of 0-3).
The difficulty of 8 of 30 items of the CHAQ depends on the respondent's age. Nevertheless, the design of the CHAQ and its scoring system remove most of the expected physical development bias.