A Statistical Method of estimating the Periods of Incubation and Infection of an Infectious Disease

Abstract

CERTAIN infectious diseases are supposed to have relatively constant incubation periods with short intervals of high infectivity. Greenwood¹ studied an idealized model, having a fixed incubation period and point-infectivity. He showed that a single primary case in a small family group of susceptibles would lead to a chain of binomial distributions of new cases. With measles, the observed distribution of the total size of family epidemics agreed closely with that predicted by the theory. Later, Wilson et al. ², analysing new data with respect to the actual links of each chain, obtained only poor fitting of theory to observation. Following a hint of Greenwood's³, Bailey⁴ showed that satisfactory agreement could be restored by introducing a suitable distribution for the chance of infection in different families.