Statistical analyses
Statistical analyses were performed with Stata software (version 15, StataCorp, College Station, Texas, USA) and R 3.5.1 (http://cran.r-project.org/). All tests were two-sided with an alpha level set at 5%. Categorical variables were expressed as number of children and associated percentages, and continuous variables as mean ± standard deviation or as median [25th; 75th percentiles], according to the statistical distribution and the results previously reported in the literature. Factors associated with OAHI, RS30 and RS10 were studied with: Mann-Whitney test for binary variables, Kruskal-Wallis test for categorical variables with more than two categories and Spearman’s rank correlation coefficient for continuous variables. To assess whether RS30 and RS10 can be predictive of an OAHI ≥ 1.5 and ≥ 5, receiver operating characteristic (ROC) curves were plotted. The area under the ROC curves were presented with a 95% confidence interval (CI) obtained with the technique of DeLong et al[21]. Finally, Youden’s index was calculated to study the “optimal” threshold value of RS30 and RS10 to predict an OAHI ≥ 1.5 and ≥ 5. It was presented with its specificity, sensitivity, and negative and positive predictive values.