Those methods can be applied to any epidemiological study based on serology, within human or animal host populations. Applied here to feline viruses, they revealed significant associations between three pairs of feline viruses. If they still do not allow us to decide whether such associations are really true interactions or whether they reveal the existence of ''over-susceptible'' hosts, we believe it is an important step forward as it offers the possibility to point out parasites associations that should be further investigated in experimental conditions. The understanding of parasites interactions and of their consequences on diseases evolution, emergence and management is indeed a crucial challenge for human and animal epidemiologists of our time. Figure S2 Issue of the conformity tests of the type I error to 5% according to the N F /n ratio for the logistic regression approach. The issue was coded 1 when the test was significant, 0 when not and the resulting logistic regression was drawn (dark line). Three scenarios are considered: i) all factors are qualitative (A); ii) all factors are quantitative (B) and iii) half of the factors are quantitative and the other half are qualitative (mixed scenario, C). (EPS) Figure S3 Type I error (%) of the corrected chi-square tests according to the N F /n ratio and the type of P-value used for the corrected chi-square: P-value1 (blue empty points) or P-value2 (red full points). Three scenarios are considered: i) all factors are qualitative (A); ii) all factors are quantitative (B) and iii) a half of the factors is quantitative and the other half is qualitative (mixed scenario, C). The dashed horizontal line represents a type I error of 5%.