Statistics
tracheal cartilage injury
Pearson chi-square tests were applied using SigmaStat 3.5 program (Systat Software Inc., San Jose, CA, United states) for statistical evaluation. To calculate the sample size of the study, the frequency of tracheal cartilage injury was the variable of interest. We assumed that a minimum of 20% difference was considered clinically important, and that in combination with our previous results of 9% from earlier experiments were used for the calculations. [13] A type one error of 0.05 and a required (statistical) power of 0.80 were set. A minimum of 150 cadavers were required based on the conditions detailed above.