Fig. 1.

A recreation of William Farr's possible approach modeling the decline in smallpox mortality in England, 1837–1839 (Farr, 1840). Black line, smallpox mortality by season; gray dots represent Farr's “model projections” derived by assuming a constant additive increase (approximately 5% per season) in the decline in smallpox deaths. Farr “smoothed” reported seasonal deaths by averaging adjacent seasons; hence model projections are plotted at the midpoint (e.g., “winter-spring”, “spring-summer”) at each interval.