[Logistics regression in epidemiology. II].

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 as quantitative variables. According to this model, the probability of disease knowing Xi's values is written: [formula: see text]. The coefficients 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 second part of this paper is devoted to the tests of hypothesis in the logistic model and to the choice of the variables to be included in the model. The way of using tests to decide how to code variables is explained. Analysis strategy (choice and selection of variables) is discussed. The rational of goodness of fit tests is shown. At least, we indicate how to use the logistic model in case-controls studies and in studies with matched samples.