Linear regression analysis of probability[at least one mutation is mutagen-induced | cancer occurs] (dependent variable) versus log10[cumulative stem cell divisions] (independent variable).

The conditional probability is evaluated (via expression (9)) using a generalization of the model of Wu et al. [11] using k = 1 to 4 critical cancer mutations, a spontaneous mutation rate of uS = 10−8 per cell division, and a mutagen-induced mutation rate, uM = 2 x 10−9, 5 x 10−9 or 1 x 10−8 per cell division, mutagen-associated rates increase from 0 after the first third of stem cell divisions. The data used in the regression are given in Table A1 in S1 Appendix.