The Childhood Health Assessment Questionnaire (CHAQ) is the most widely used functional health status measure in children with Juvenile Idiopathic Arthritis (JIA)[1, 2]. It assesses functional ability in 8 domains of physical function (30 items) for children between the ages of 6 months up to 18 years. Each item is scored on a four point scale ranging from 0 (without any difficulty), 1 (with some difficulty), 2 (with much difficulty), 3 (unable to do). Utilization of assistance and or aids in a domain sets the score to a minimum of 2 for that domain. The mean score of the eight domains finally makes up the disability index and ranges from 0 (no disability) to 3 (disabled). The disability index is supplemented with two visual analogue scale (VAS) scores: one for pain, and one for global assessment of overall well being.
Although originally designed to be used as an outcome measure in childhood rheumatic diseases, the CHAQ is currently used in other conditions such as spina bifida and juvenile dermatomyositis[4, 5]. Over the past decade, as a result of improved treatment strategies , the CHAQ suffers from a ceiling effect. The most noticeable consequence of this ceiling effect is that it is impossible to measure improvements at the better end of the functional spectrum. In other words, clinical validity is reduced.
For this reason researchers have recently took up the challenge to introduce and test suggestions for revision of this instrument to improve its psychometric properties. Lam et al. , for example, examined the discriminative validity and score distribution of three new versions of the CHAQ. One important aspect of these versions was ignoring both the domain structure and use of aids and assistance. These new versions proved to enhance discriminative validity of the CHAQ in a Canadian cohort of children with a wide diversity of musculoskeletal conditions. In addition, Takken et al.  performed thorough statistical procedures and concluded that two manoeuvres could enhance the psychometric properties of the CHAQ. Firstly, by removing twelve redundant items, and secondly, by ignoring the domain structure and the use of aids and assistance. In addition, a recent cohort study in 2663 patients showed that removal of aids and assistance from the CHAQ did not change the interpretation of disability at a group level. Therefore the authors conclude that a CHAQ without these items is a more feasible and valid alternative for the evaluation of disability in JIA patients .
The encouraging findings of Lam et al. have resulted in efforts to replicate them in Dutch populations. Ouwerkerk et al.  examined the score distribution of several revised versions of the CHAQ in a partial retrospective study. In extension of this work Van Dijk et al.  examined the score distributions of new versions prospectively in children with JIA, in a Dutch multi centre study. Results of these studies are comparable to those of Lam et al. and encouraged further investigation into a broader cross cultural context. As a result, the aim of this prospective cross-sectional European multi centre study was to explore the score distribution of 4 different versions of the CHAQ in different European languages. Three revisions of the CHAQ were of major interest in the current study, namely, 1) the addition of 8 more challenging items, 2) ignoring the scale structure and aids and assistance, and 3) the effect of a new categorical response option, that allows patients to rate themselves not only worse than their peers, but even better at activities than most other children and young people their age.
Our specific hypothesis is that the addition of the 8 more challenging items and a new response option enhances discriminative validity and has a positive influence on the score distribution of the CHAQ compared to the original CHAQ.