Finally, to emphasise the need to consider risk factors in the analysis of interactions, we also calculated the classical independence Pearson's chi-square. This approach, which does not integrate risk factors, predicted an association between five of the six tested pairs. In the case of the FIV-FCV and FIV-FHV pairs, it would lead to wrongly conclude on the existence of an interaction, whereas the two approaches have shown that these apparent interactions were in fact explicable by shared factors.