Statistical Analyses
Statistical analyses were performed with R software (2020, version 4.0.0, R Core Team, Vienna, Austria). Data on patient demographics, comorbidities, and management were presented with proportions for categorical data and medians with an interquartile range (IQR) for continuous data. Subgroup analyses were performed for patients presenting with only CSU and patients presenting with CIndU (regardless of co-existing CSU). To ensure the validity of the UCT among children in whom the CDLQI is validated, a subgroup analysis was performed in patients aged 4 to 16 years.
Internal consistency of the UCT was evaluated by Cronbach’s α coefficient, calculated by the Psych package. Cronbach’s α coefficient was interpreted as follows: <0.60 unacceptable, 0.60-065 not desirable, 0.65-0.70 minimally acceptable, 0.70-0.80 respectable, 0.80-0.90 excellent, and >0.90 excessive redundancy17.
Convergent validity of the UCT was assessed by Pearson partial correlation with the CDLQI using the ppcor package in groups with ≥25 patients18. Partial correlations were controlled for sex and age. The following strata were used to interpret r values: 0.90-1.00 very strong correlation, 0.70-0.89 strong correlation, 0.40-0.69 moderate correlation, 0.10-0.39 weak correlation, and 0.00-0.10 negligible correlation19.
Known-groups validity of the UCT was assessed by the Kruskal-Wallis test using established CDLQI disease severity strata: 0-1 no effect, 2-6 small effect, 7-12 moderate effect, 13-18 very large effect, and 19-30 extremely large effect20.
We considered a CDQLI cut-off value of ≥6 as indicative of poorly controlled disease21. Using this cut-off, we assessed the screening accuracy and the area under the curve (AUC) of the UCT in the identification of poorly controlled CU by receiver operating characteristics (ROC) curve via the pROC package. Optimal UCT cut-off values were estimated by the Youden index22. AUC values were interpreted according to the following cut-off values: ≥0.90 outstanding, 0.80-0.89 excellent, 0.70-0.79 acceptable, 0.50-0.69 poor, and 0.50 no better than chance23.
Bootstrapping hypothesis testing with 100, 000 iterations was used to evaluate the change in UCT scores from study entry to follow-up between patients who started or increased their dose of sgAHs versus patients who decreased their dose or ceased sgAHs.