Abstract

Data from historical epidemics provide a vital and sometimes under-used resource from which to devise strategies for future control of disease. Previous methods for retrospective analysis of epidemics, in which mooted interventions are compared, do not make full use of the information; by using only partial information on the historical trajectory, augmentation of control may lead to predictions of a paradoxical increase in disease. Here we introduce a novel statistical approach that takes full account of the available information in constructing the effect of mooted intervention strategies in historic epidemics. The key to the method lies in identifying a suitable mapping between the historic and notional outbreaks, under the mooted control strategy. This is done by using the Sellke construction as a latent process linking epidemics. The application of the method is illustrated by two examples. First, using temporal data for the common human cold, the improvement under the new method in the precision of predictions for different control strategies is shown. Secondly, the generality of the method for retrospective analysis of epidemics is shown by applying it to a spatially-extended arboreal epidemic in which the relative effectiveness of host culling strategies that differ in frequency and spatial extent are compared. Some of the inferential and philosophical issues that arise are discussed along with the scope of potential application of the new method.