[Causal research epistemology and epidemiology of complex systems]

Epidemiology now meets with the crisis of its most fundamental paradigm. The biomedical paradigm of the search for individual-level disease risk factors opposes the public-health paradigm of the search for contextual-level disease risk factors. The public-health paradigm exacerbates the causal research of disease risk factors in that it must now count on a hierarchy of scales of observation. This underlines the need to take into account nonlinear relationships among scales and variables as well as the dynamic aspect of the phenomena. It is concluded that the complex conceptualization required by the public-health paradigm will entail epidemiologists to develop new theories and to familiarize themselves with approaches more akin to those used in the study of complex systems.