Statistical Analysis

Continuous variables were presented as mean (standard deviation) or median (interquartile range), depending on their distributions. Groups were compared with the t-test if normally distributed and the Mann–Whitney U-test if not. Categorical data were presented as frequencies and percentages and analyzed using 2-tailed χ2 tests or the Fisher exact test. For the primary outcome of delirium, the two groups were compared with the χ2 test for differences in probabilities of a 2×2 contingency table. Risk ratio (RR), risk difference (RD) and difference were reported with 95% confidence intervals (CIs). All statistical tests were 2-sided and a value of P < 0.05 was considered to be statistically significant. Statistical analyses were performed using SPSS version 24 (IBM, Armonk, NY, USA).