2.4. Statistical Analysis

Statistical data processing was performed using the Statistica 6.0 software. To check the normality of the distribution for the quantitative parameters, the Kolmogorov–Smirnov test was used. The results of statistical analysis of data with nonnormal distribution were presented as median, upper, and lower quartiles. Statistical significance of the differences was calculated using Mann–Whitney U test. The correlation analysis was done using Spearman's correlation coefficient (r). The p-value of less than 0.05 was considered to be significant. The receiver operating characteristic (ROC) curve was calculated to measure the sensitivity and specificity of the level of TLR2 expression on circulating CD4⁺ cells as a diagnostic and prognostic biomarker for COPD. An area under the ROC curve (AUC) with a 95% confidence interval (CI) was evaluated. A probability of p < 0.05 was considered as the threshold of significance.