Statistical Analysis
Descriptive statistics for clinical and demographic characteristics of the patients are presented as frequency and percentage (%) for categorical variables and mean with standard deviation (mean ± SD) or median with interquartile range (median [Q3–Q1]) according to the distribution of the continuous variables. The normality was assessed both visually and through the Shapiro–Wilk test. The independent samples t-test was used to evaluate the intergroup differences for normally distributed data; lung volumes and densities. For the parameters which were not normally distributed, Mann–Whitney U test (Wilcoxon rank-sum test) or Kruskal–Wallis test was used as appropriate. Pearson Chi-square test was applied to analyze the categorical variables. The Spearman’s rank correlation coefficients were used to examine the degree of associations between the right and left lung densities, and right and left lung volumes and FVC and DLCO [13]. The test-retest reliability was assessed by the intraclass correlation coefficient (ICC). The strength of agreement between repeated measures was determined by an ICC of 0.7 or greater, representing a high agreement [14]. Statistical analyses were performed using the SPSS, version 20.0, software (IBM Inc., Chicago, IL, USA) and RStudio, Version 1.2.1335© 2009-2019 (PBC, Boston, MA). Two-sided p values less than 0.05 were considered statistically significant (p <0.05).