2.2 Statistical Analysis
Data are presented as mean ± standard deviation if normally distributed or as median values and interquartile range. Continuous variables were tested with the Kolmogorov-Smirnov test for normal distribution. Categorical variables are given as frequencies and percentages. A chi-square test was used for comparison of categorical variables between the groups. Student’s t-test and One Way ANOVA was performed for comparison of normally distributed continuous variables. For non-normal distribution variables we used Mann-Whitney U test and Kruskal-Wallis
To explore the independent association of tracheostomy timing on mortality, we used the multivariate multivariable Cox Proportional hazards model with time-dependent covariates. In the multivariate analysis, we included covariates that differed significantly in the univariate. Therefore, the Cox Proportional hazards model included the following covariates: age, sex, morbid obesity, smoking, and tracheostomy timing.
Statistical significance was assumed when the null hypothesis could be rejected at p < 0.05. All P-values are the results of two-sided tests. Statistical analyses were conducted using SPSS (version 27).
3. Results