A Simulation-based Study Comparing A Traditional and An Alternative Design for Studies of Experimentally Induced Intestinal Diseases in Pigs

By Emanuelson, U. - Waern, M.J. - Jacobson, M.

A traditional design for studies of pathogenesis of experimentally induced diseases of the large intestine in individual pigs involves euthanasia and necropsy at scheduled times. An alternative design has been developed enabling the sequential in vivo monitoring of events in the intestine of the individual pig before and during disease. The alternative design is based on repeated endoscopy and biopsy sampling to monitor the course of the disease. The purpose of this study was to compare the statistical properties of the two designs. One hundred replicates of a computer-generated simulation of data were performed. In the simulation, data were generated for individual pigs according to the alternative design, i.e. four sequential observations on the outcome of interest, and the 'traditional' design was created by retaining only one observation per pig. Data from the alternative design were analysed with a generalized linear mixed model, accounting for the clustering of observations within animals and the time-dependence between observations within animals, i.e. observations within animals are interdependent and follow a pattern over time. Data from the 'traditional' design were analysed with an ordinary linear model. The results showed that the alternative design was much more efficient than the traditional and that only one-fourth as many pigs were required to achieve the same precision in estimated effects.