Spss 26 statistical

Data were analyzed using SPSS 26 statistical software (IBM SPSS Statistics) and R software version 4.1.2. Continuous variables were expressed as mean ± one standard deviation (SD), while categorical variables were expressed as number (frequency). We used the Shapiro–Wilk test to test the normal distribution of continuous variables. We then used the Mann–Whitney U or Kruskal–Wallis tests to compare the mean values of two or more than two groups, respectively. For comparison of categorical variables, we used either Fisher's exact test or Pearson’s chi-square test, as indicated^{32 (link)}. Wilcoxon matched-pair signed-rank test was used to compare the median values of the paired samples. Moreover, the Spearman correlation coefficient was calculated to examine the correlation between ROI-ADC and the Ki-67 index. A stepwise backward multiple linear regression that included possible confounding variables (such as, patient age, tumor LD, hormonal receptors status, HER2 status, immunohistochemistry results, SBR grade, and δADC) for the prediction of the δKi67 proliferation index after NACT and a multivariate logistic regression to predict pathologic response were done. ADC and Ki67 proliferation index variations (δ) were calculated as follow: (value before NACT − value after NACT)*100/value before NACT. Statistical significance was assumed when the p-value was < 0.05.