Chapter 6 104 Statistical analysis Continuous data were reported as median (interquartile range) and categorical data as count (percentage). The strength of agreement between mrTRG after completion of neoadjuvant treatment and the pathological response rate was assessed using the weighted kappa test (k value<0.20: poor agreement; k value=0.21–0.40: fair agreement; k value = 0.41–0.60: moderate agreement; k value = 0.61–0.80: good agreement; k value=0.81–1.00: very good agreement). This analysis was performed using the five categories of tumour regression, as well as using a two-tier regression scale, adapted from these standardised five-tier regression scales, i.e. Mandard 1-2 (good responders) versusMandard 3-5 (intermediate/poor responders) andmrTRG 1-2 versusmrTRG3-5. The interobserver variability between the two radiologists regarding the assessment of mrTRGwas analysed using theweighted kappa test, considering the five-tier regression scale as well as the two-tier regression scale (mrTRG 1–2 versus mrTRG 3–5). Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of mrTRGwith regard to the pTRGwere calculated from two-by-two contingency tables using predefined categories (mrTRG 1-2 versus mrTRG 3-5 and pTRG 1-2 versus pTRG 3-5). All statistical analyses were performed using IBM SPSS Statistics version 25.0 for Windows (IBM Corp, Armonk, NY, USA).
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