Statistical Methods and Analysis
Primary stratification was between males and females who underwent ATAAD
repair. Continuous variables were presented as mean ± standard deviation
for normally distributed data, or median and interquartile range (IQR)
for non-normally distributed data. Categorical data were reported by
frequency and percentage. Normally distributed continuous variables were
analyzed using the student’s t-test, while non-normally distributed
continuous variables were analyzed with the nonparametric Mann-WhitneyU test. The Chi-squared or Fisher’s exact test was used to
compare categorical variables between groups, as appropriate. Unadjusted
survival estimates were generated using Kaplan-Meier methods and
compared using log-rank statistics. A Cox proportional hazards
regression model was used for the multivariable analysis of mortality.
The assumption of proportional hazards was validated using Schoenfeld
residuals, and, for covariates other than sex in the model, the method
of stepwise selection was employed with a threshold of inclusion in the
model of p<0.020.
Supplementary propensity score matched analyses were performed using
greedy nearest neighbor caliper matching, with calipers of width setting
at 0.2 of standard deviation. Propensity score matching incorporated the
following variables: patient age, history of hypertension, history of
chronic lung disease, performance of hemiarch replacement, and
performance of total arch replacement. All statistical analyses were
performed using SAS/STAT Version 15.2 (SAS Institute Inc., Cary, NC,
USA). All tests were 2-sided with an alpha level of 0.05 designated to
indicate statistical significance.