Statistical analysis:
The patients were divided into three age categories: preschoolers (≥3 yr and <6 yrs), schoolchildren (≥6 yrs and <12 yrs), and adolescents (≥12 yrs and ≤17 yrs). We identified the presence of the inversion of the reactance curve (Figure 1), and we measured the lineal tendency of the percentage of patients that required X5 approx. correction according to the age categories, using the Mantel-Haenszelײ test. We analyzed the difference between patients with and without inversion of the reactance curve and X5 correction in the percentage of IOS alteration parameters. Then we measured the mean differences of IOS and FEF25-75% between the groups of patients with and without X5 approx. correction. Also, the correlation of X5 and X5 approx. with the other IOS basal parameters in each age category was measured. The differences in % of basal parameters in IOS were calculated using the Fisherײ test or the Pearson test with the Yates correction, where appropriate. For measuring the mean difference between patients with and without X5 approx. correction, the t-student test for an independent sample was used, and for the correlation of X5 and X5 approx. with the IOS and spirometry parameters, the Pearson correlation test was used. In both analyses, normal distribution was verified.
The sample size for establishing the difference between groups without X5 and with X5 correction was calculated in accordance with the pilot study, and 380 patients were needed with 80% of power and 0.05 alfa. For the statistical analysis, SPSS® v17.0 (IBM, Armonk, NY) software was used.