With all three, however, the challenge is the same: journalists must explain that epidemiology is probabilistic, rather than absolute; that it is about chance, not certainty. With every story, reporters must precisely describe the likely consequence of any action -doubling or halving the risk of heart disease, for example. They must describe any internal factors that affect confidence in the study - the bigger the population and the longer the period of time examined, the better. And they must describe any external factors that affect confidence in the study - that is to say, the number and strength of supporting or competing hypotheses.

Curtis Brainard is the editor of The Observatory, CJR's online critique of science and environment reporting. Follow him on Twitter @cbrainard.