
105Implementation
An interesting example of a special entity was implemented in a model
assessing various vaccination strategies to prevent bacterial meningitis epi-
demics (Caro etal. 2007). The validation work for that model showed that
the outbreaks of disease occurring in the simulation were less frequent than
those observed in available epidemiologic data, despite careful construction
of the risk equations. Rather than calibrating the equations to the new data, a
special event was incorporated that triggered a change in the force of infec-
tion, increasing the chance of an outbreak. The sole purpose of the special
Outbreak Demon entity was ...