Minimal clinically important differences of the childhood health assessment questionnaire

The Childhood Health Assessment Questionnaire (CHAQ) is a commonly used measure of disability and physical function for children with juvenile rheumatoid arthritis (JRA), whose scores range between 0 (no disability) and 3 (very severe disability), with a smallest potential difference in the CHAQ score of individuals at 0.125. We estimated minimal clinically important differences (MCID) of the CHAQ for worsening and improvement that were actually experienced by children with JRA using patient, parent, and clinical perspectives.

Changes in CHAQ scores were calculated for parent (n = 92) and patient ratings (children age > or = 8 yrs only; n = 67) between subsequent clinic visits. Changes in patient well being and disease activity and the occurrence of flare or important improvement between visits served as external standards for the MCID. MCID were defined as the median changes of the CHAQ scores of individual patients who had a minimal important improvement or worsening between visits.

The median change in CHAQ scores of patients who rated themselves or were rated by others as unchanged was often 0. Depending on the external standard used, the MCID for improvement of the CHAQ was -0.188 at most, while the MCID for worsening was at most +0.125.

The MCID of the CHAQ for both improvement and worsening are often at or close to the level of the smallest potential difference, suggesting that the CHAQ is relatively insensitive to important short term changes in children with JRA. This may warrant a change in the calculation of the global CHAQ score, or the development of more sensitive functional measures.