The distribution of incubation periods of infectious disease. 1949.

1. Characteristics of the distribution of incubation periods of a number of infectious diseases, as reported in the literature, have been reviewed. 2. The usual frequency curve of incubation time takes the form of a logarithmic normal curve. This appears to be equally true of diseases with very short and very long incubation periods. 3. The measure of variation in incubation periods used in this study, termed the dispersion factor, is the antilogarithm of the logarithmic standard deviation. Dispersion factors for most of the diseases studied range from 1.2 to 1.5 and are independent of mean length of incubation. 4. Some epidemiological uses for a knowledge of the distribution of incubation time are discussed.