| Abstract: | By modelling the progression of the avian disease caused by Newcastle disease virus (NDV) as a one‐step, time homogeneous Markov Chain (MC) it is possible to set the intracerebral pathogenicity index (ICPI) in a statistical context. Previous assessments of ICPI values for different viruses ignore the fact that the same ICPI value may occur via different sequences of disease status. However, the MC model approach takes into account the state transitions by which an animal came to obtain its particular contribution to the ICPI value. Because the probability that an animal remains normal approaches zero as time increases, the MC model suggests a pathogenicity index based on the multiplying factor that determines this probability's approach to zero. Numerical examples are given with data from NDV pathogenicity trials. |
