Minimally important change in a parent-proxy quality-of-life questionnaire for pediatric chronic cough

Background: The Parent Cough-Specific Quality-of-Life questionnaire (PC-QOL) has relevance and clinical utility as a cough-specific QOL measure for pediatric use. Its validity has been demonstrated. This study sought to determine the minimally important difference (MID) for the PC-QOL completed by parents of young children with chronic cough.

Method: Thirty-four children (22 boys, 12 girls; median age, 26.5 months; interquartile range, 17.3-38.8 months) and their mothers participated. Mothers completed a cough-related measure (verbal category descriptive score) and the PC-QOL on two occasions separated by 2 to 3 weeks. Two approaches were used to calculate MID. 

Results: Distribution-based approaches to estimating MID resulted in ranges of 0.50 to 0.78 (effect size method), 0.30 to 0.48 (SE of measurement method), and 0.60 to 0.69 (one-half SD method) for PC-QOL overall and domain scales. Based on verbal category descriptive score change, an anchor-based approach resulted in an MID estimate of 0.9 for overall PC-QOL change and ranged from 0.71 to 0.95 for individual domain PC-QOL change. 

Conclusion: An MID for the PC-QOL of 0.9 is recommended in interpreting health status change in children with chronic cough and will aid clinicians and researchers in interpreting health-related QOL changes following treatments and clinical trials.