One historically interesting example may help. Florence Nightingale thought it was crucial that soldiers in the crimean war be given clean linens, clean dressings, and fresh air. She saw with her own eyes that this greatly reduced gangrenous post-operative infection. She also totally rejected the new idea that living agents referred to as “germs” by the scientist Louis Pasteur might be playing an important role. So, paradoxically, she notes a correlation between clean dressings and better infectious disease outcomes all the while rejecting the proposed cause, a cause which is now absolutely non-controversial except among certain groups of chiropractors who still deny the germ theory of disease.

Even so, within this group of relatively benignly behaved individuals, clear differences are seen, and those differences are of a dose-response relationship (higher dose equals higher likelihood of outcome: cancer death, cardiovascular death, all-cause death). The authors went to great lengths to tease apart the differences related to smoking and to some lengths to tease apart the differences due to exercise.

makes me think that the people in the study who ate more red meat had less healthy lifestyles in general.

The point of the stats post and what we’ll write more about today (hopefully, time willing), is that correlation can, when it is well done, allow us to meaningfully infer causation (smoking and cancer being, of course, the poster boy for this). Basically, saying correlation doesn’t equal causation is correct, yet not always accurate in practice. Do note the study authors make absolutely no claims about causation, not a one. We can’t prove to absolute scientific certainty that there is a link between consumption of certain meats and certain bad health outcomes… but we can show a freaking huge study over a huge span of time and say, we’ve met all the criteria for strong inference, and hey, we’re not 100% (and never will be because you can never perform experimental, lab research on this), but it’s pretty darned suggestive, no?

Dismissing r studies’ findings because they are not controlled laboratory experiments is a narrow conception of how research is done and how we come to know our world. It all comes down to the particular study and how well it is done, how much we can infer, is there complimentary research we can look at for confirmation or discomfirmation, etc. This study is one big piece of a larger puzzle about human health.

Also, I think I missed the part in the paper where they say eating meat causes AIDS (or if that was a joke it is too early in the morning for me to get it, apologies). Brain still foggy… did you mean interpretations in the popular press are taking this way too far and making wild assumptions based on it? If so, yeah, the state of science journalism sucks big time.

Quick clarification of what I was getting at, which was not even vaguely “why should I care?”. This is a study which says, basically, the people who eat less meat seem to live longer then people who eat more meat. Now there are a ton of things one can take from that, but all of those things must be taken with the understanding that “correlation does not necessarily equate to causation”.