Chain-binomial models: Models arising in mathematical theory of the quite infectious diseases, which postulate that at any stage in the epidemic there are a certain number of the infected and susceptibles, and that it is reasonable to assume that the latter will yield a fresh crop of cases at the next stage, the number of the new cases having a binomial distribution. This results in the 'chain' of binomial distributions, the real probability of the new infection at any stage depending upon the numbers of infectives and susceptibles at the prior stage.