[Longitudinal study of the evolution of the frequency of dental caries in a school milieu: a statistical model]

Following a 3-year epidemiological study of the appearance of dental caries in a population of children aged 6 to 9 years (and examined every 12 months), a model of the evolution of the frequency of caries based on a Poisson "with zeros" distribution is proposed. The multivariate distribution of the above phenomena appears as a mixture of multiple negative binomial distribution (MNB) of the following form: sigma mjMNB(a;k0jb,k1jb,k2jb) with sigma mj = 1. The experimental data from the sample of 501 children validate the model in its successive stages. Simulations using the bootstrap method show that the estimates of the model parameters remain stable in the neighbourhood of the distribution observed; at the same time they permit establishing the margins of confidence. Finally, it is shown why the total number of dental faces affected during the experimental period remained strongly asymmetrical.