Statistical analysis
Statistical analysis was performed with SPSS 18.0 software for Windows
(SPSS, Chicago, IL, USA). The Kolmogorov-Smirnov test was used to
determine whether variables were normally distributed. Normally
distributed data are described as means±standard deviations (SDs). Group
differences were analyzed by Mann-Whitney tests (for non-normally
distributed data) or analysis of variance (ANOVA). Differences between
categorical variables were assessed by the χ2 test. Simple linear
regression analysis was performed by Spearman’s rank correlation test. A
p-value < 0.05 was considered as statistically significant.
Sample size
determination
The minimum sample size was computed with respect to a two-tailed,
one-sample Student t-test considering, on the basis of data from a
previous pilot study (data not shown): a difference of 8 pg/ml for H2O2
levels between children affected by VKC and controls, 5.5 as SD, 0.05
(α) as type I error probability and 0.95 as power 1 − β. The sample size
was n = 10 patients/group.