A potential cause of the reported increase in rates of autism

Thank you for republishing the landmark paper by Cornfield et al., which the late George Comstock felt should be read by all epidemiologists at least once per year. Of the many innovative aspects for which this paper is praised, we would like to add here one that is rarely mentioned. Appendix B of the paper provides the algebraic proof of an important property of risk ratios described in the body of the paper as follows: