PR analysis of 1H-NMR spectra between different stages of esophageal cancer and normal mucosae. A, scores plot of OPLS-DA model processing based on each stage and normal mucosae, red dots represent stage II (n = 28); blue boxes represent stage III (n = 45); purple diamonds represent stage IV (n = 16) and black triangles represent normal mucosae (n = 26). B, statistical validation of the corresponding PLS-DA model by permutation analysis (200 times). R2 and Q2 represent the predictive ability to the model. C, scores plot of OPLS-DA prediction model. 80% of samples were applied to construct the model, and then used it to predict the remaining 20% of samples (normal mucosae = 5; stage II: n = 5; stage III: n = 9; stage IV: n = 3). Green diamonds represent normal mucosae and yellow inverted triangles represent esophageal cancers.