In his article "Science pseudoscience nutritional epidemiology and meat" http://garytaubes.com/2012/03/science-pseudoscience-nutritio... Gary Taubes discusses how epidemiological studies can fail to account for something called the "compliance effect" - the missing variable.
He quotes a textbook chapter in his conclusion. So the idea that you have to at least be careful with your statistics is orthodoxy, not some missing component of the field.
(I realize that doesn't make any guarantees about common practices, but it is maybe a little capricious to repudiate the entire field)
It was an eye opener for me.