Statistical analyses
cognitive failure
We carried out a sample size calculation for the primary outcome of our study (cognitive training–related effect on objectively assessed cognition), which was published in advance (Butz et al., To determine the effect of cognitive training on cognitive failure in daily living and health‐related quality of life, we conducted analyses of covariance (ANCOVAs) with the postoperative questionnaire value as the dependent variable, groups (control group/training group) as the fixed factor, and the preoperative questionnaire value as the covariate. We tested assumptions for ANCOVAs using the Levene test (homogeneity of variance between groups) for the dependent variable and a statistically significant correlation between the dependent variable and covariate (preoperative test value) calculated using the Pearson product‐moment correlation. As a further assumption, we checked the distribution and Q‐Q plots for normality. When assumptions for ANCOVA were violated, we calculated difference values between pre‐ and posttests, followed by the Mann–Whitney Subjective‐POCD was defined as a decline and subjective‐POCI as an improvement from pre‐ to postassessment of at least 1 SD (Kastaun et al., We give the effect size as 