When we already have epidemiology about the health risks from an exposure, drawing conclusions about risks based on toxicology or similar sciences is like drawing conclusions about what the weather was yesterday by looking back four or five days at what the forecast for yesterday was.
That is, these other sciences, if used properly (a big “if”), can offer the best possible guess about what an unknown health risk will turn out to be, and depending on the specifics it might be a very rough guess or a pretty good one. But how much sense does it make to use the guess about what the result would be when you already have seen the result, which is to say, when we already have good epidemiology? It might be useful if there was an observed risk and we wanted to figure out what was causing it. But to make claims based on toxicology about whether there is a substantial health risk under those circumstance demonstrates the same mastery of scientific reasoning as reporting whether it rained yesterday based on last week’s forecast.
The most obvious example to many of my readers will be the anti-harm-reduction people who keep looking at the chemistry of smokeless tobacco in order to determine …well…um (or should I say umn)… Well, as best as I can tell, they are trying to determine the cause of the apparently non-existent cancer risk. (Ok, the epidemiology can only show the risk is too small to measure, not that it does not exist at all, of course. But it zings better with the over-simplification.) The absurdity of that, however, does not stop them from trying to mislead the public into believing that they produced evidence of actual risk (you would think that if someone was so desperate to be doing epidemiology they could probably make the change and do epidemiology).
The same error in the opposite direction is made by the acousticians, the equivalent of toxicologists when the exposure is sound rather than chemicals, (and, sadly, those who believe them and make important decisions – a link to recent news, btw, to keep up the spirit of the series) who cannot figure out how wind turbines could cause health effects. Since there are thousands of useful reports about turbines causing serious health effects, that “we cannot figure out how” obviously translates into “we should try to figure out how” rather than “our ignorance is evidence that there is nothing happening”. Yet they manage to say, in effect: Who are you going to believe, our theoretical models or your own lyin’ ears?
Indeed, the latter example is arguably worse. At least the toxicologists predicting non-existent cancer are following a bad recipe for concluding that it rained yesterday (something you have a record of, but still need to gather information about) when the records show that it did not do so. The acousticians who claim that wind turbines cause no health problems, despite so many people observing their stress reactions when they are near moving turbines, are more like someone who concludes, based on last week’s forecast, that it is not raining right now, despite the mysterious presences of droplets of water falling past the window.