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