2.2. Statistical analysis

Statistical Program for Social Sciences 20 (IBM SPSS, Chicago, IL, USA) was used for all statistical calculations. Kolmogorov-Smirnov test was used to check whether the data were normally distributed. Continuous variables were expressed as mean ± SD or median (interquartile range) and compared with Student's t or Mann-Whitney U tests according to normality. Categorical variables were expressed as percentages and numbers and compared with the Chi-square test. Univariate regression analysis was performed to identify possible risk factors affecting prognosis. In addition, multivariate linear regression analysis was performed to identify independent predictors of prognosis. Receiver operating characteristic (ROC) curve analysis was used to determine the optimum threshold value of frontal (QRS-T) angle level for predicting prognosis in patients with COVID-19. p < 0.05 was accepted as statistically significant in all analyses.