Farr's law applied to AIDS projections
D. J. Bregman and A. D. Langmuir
Department of Preventive Medicine, University of Southern California, Los Angeles 90033.
Farr's Law of Epidemics, first promulgated in 1840 and resurrected by
Brownlee in the early 1900s, states that epidemics tend to rise and fall in
a roughly symmetrical pattern that can be approximated by a normal
bell-shaped curve. We applied this simple law to the reported annual
incidence of cases of acquired immunodeficiency syndrome in the United
States from 1982 through 1987. The 6 years of incidence data closely fit a
normal distribution that crests in late 1988 and then declines to a low
point by the mid-1990s. The projected size of the epidemic falls in the
range of 200 000 cases. A continuing incidence of endemic cases can be
expected to emerge, but we believe it will occur at a low level.
