PCA scores plots from models created using spectral data for some postoperative time point versus the preoperative spectra. Each model had 3 PCs; (a) 1 hour after operation ( and ); (b) 2 hours after operation ( and ); (c) 24 hours after operation ( and ); (d) 48 hours after operation ( and ); and (e) 72 hours after operation ( and ). Open shapes are preoperative samples, and filled shapes are postoperative samples. Black triangles represent patients who scored lATs, and red squares represent hAT patients. The dashed line represents the visual divide between pre- and postoperative samples, and the solid line and dashed ovals are for ease of visualisation of grouping of lAT and hAT patients, respectively, and are not statistically relevant. The main solid black ellipse surrounding the majority of the scores in each plot is Hotelling’s T² elliptical tolerance region, which indicates the 95% confidence limits. These plots show a clear separation between pre- and postoperative samples which diminishes with time. Furthermore, hAT patients are more tightly clustered than the lAT patients, who appear to split into two groups.