Results of the logistic regression for the case-case studies.

(A) Odd ratios and their associated P–value for all the selected cases in the univariate models. Factors with P<0.05 are considered as significant (*). Factors with a P<0.25 are entered in the multivariate model (†).
(B) Odd ratios and p-values for the final multivariate models. Previous steps, consisting in removing one by one the factors with the highest p-Value at each step, are not shown. The program used to execute the analysis gave P = 0.0060 for the overall model fit for the chicken versus non chicken case-case study, and P = 0.0006 for the C. coli versus C. jejuni case-case study. Because gender is the only factor kept at the end of the multivariate model in the chicken versus non chicken study, odd ratio and P-Value are the same as in the univariate gender model.
aAnimals are grouped into four density groups (see File S1) and the odds ratio indicates the relative amount by which the odds of the outcome changes when the value of the predictor value is increased by 1.0 unit.