[Logistic regression and epidemiology. I].

The logistic regression is used in epidemiology to study the relationships between a disease in two modalities (diseased or disease free) and risk factors Xi which may be qualitative or quantitative variables. According to this model, the probability of disease knowing Xi's values is written: [formula: see text]. The coefficients beta i satisfy to the equation: ORi = exp(beta i) where ORi is the odds-ratio linked to the variable Xi adjusted on the other variables of the model. The first part of this paper indicates the way to include in the model qualitative variables with more than two modalities, quantitative variables and interaction between variables. At least, the maximum likelihood method to estimate the parameters of the model is presented.