All data were collected from the patient charts and entered into a computerized spreadsheet. The fit of the data to the normal distribution was tested with the Kolmogorov-Smirnov test. Since the distribution of the data was significantly different from normal, nonparametric statistics were further used. Comparisons were made using Mann-Whitney U, Kruskal Wallis and Wilcoxon signed ranks tests between variables adjusted for appropriate covariates, and Spearman rank correlation coefficients were calculated between the assessed variables. The null hypothesis was rejected with a two-sided P value of < 0.05. All analyses were performed with SPSS 11.0 for Macintosh (Statistical Package for the Social Sciences. SPSS Inc., Chicago, IL, U.S.A.).