The value of uncertainty: the Zika and Microcefalia link

Scientific paradigm violations are common in the medical literature. This article aims to describe the principles that should guide scientific thinking, such as the philosophy of skepticism, the consideration of multiple hypothesis, epidemiological criteria to demonstrate association, concern about random errors and the need to quantify the strength of association. We use the hypothesis of causality between Zika and microcephaly to illustrate these principles and cognitive mechanisms that predispose to its violation. This is an example of dissociation between certainty and level of evidence, since the association between these two entities was confirmed at a time when there was no evidence of quality that supported this association.