2.3. Statistical analysis

All statistical analyses were performed using IBM SPSS Statistics 22.0 (IBM Corp., released 2013, IBM SPSS Statistics for Windows, version 22.0. Armonk, NY). The clinical characteristics of the patients enrolled in the study are expressed in numerical form. Categorical variables, which are presented as percentages, were compared using Fisher exact test and Chi-squared tests. Continuous variables are presented as the means and standard deviations and were compared using t tests. The primary goal of the study was to determine whether the clinical characteristics of patients were associated with the development of AAA. Fine and Gray's survival analysis and regression analysis were used to determine the risk of AAA (competing with mortality), and the results are presented as the hazard ratio (HR) with the associated 95% confidence interval (95% CI). Associations between time-to-event outcomes (prognoses) and clinical characteristics were examined using the Kaplan–Meier method and multivariate Cox regression analysis with stepwise selection. The results are presented as adjusted HRs with the corresponding 95% CI. Statistical significance was indicated by P < .05.