Box plots showing the predicted probabilities of lymph node metastasis for the Tokyo (a), Kyoto (b) and Seoul (c) datasets. In each figure, the boxes show the actual number of lymph node-negative (LN–) and -positive (LN+) patients, respectively. The whisker box-plots indicate the 5th, 25th, 50th, 75th and 95th percentiles (from the bottom bar to the upper bar) of the predicted probabilities. The probabilities <5% and >95% are plotted individually. The differences between LN– and LN + were statistically significant (P < 0.0001; Mann–Whitney test) in all datasets. The median predicted probabilities of LN– and LN + were (a) 33.5 (95% CI: 31.8–39.4) and 78.9 (95% CI: 69.3–80.4), (b) 33.6 (95% CI: 29.1–38.0) and 58.9 (95% CI: 49.3–62.9), and (c) 32.3 (95% CI: 28.8–35.8) and 59.9 (95% CI: 48.2–62.6).