

Understanding health studies - tokenadult
http://www.vox.com/2015/1/5/7482871/types-of-study-design

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gwern
Too bad OP didn't include one of the major specific criticisms, instead of
unconvincingly talking about the evidence pyramid: healthy-user bias.

So, the study looked at _whole-grain eating_ and a health outcome, and the
study found lower incidence of the health outcome? Who could have predicted
that? (Well, everyone. It even used the Nurses’ Health Study for data!) That
is almost as bad as the soda study a while back:
[https://news.ycombinator.com/item?id=8490522](https://news.ycombinator.com/item?id=8490522)

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tokenadult
Are you commenting in disregard of this paragraph near the top of the
submitted article? "In this case, the study population was not randomly
assigned to eat more whole grains, which means we can't know whether the
people who ate them are healthier because of their diet or because of other
traits they share, like their age, ethnicity, smoking status, alcohol intake,
physical activity levels, multivitamin use, and family medical history."

~~~
gwern
Nope. Notice that none of those is healthy user bias - age != healthy user
bias, smoking != healthy user bias, and so on. Smoking and multivitamin use
may reflect it, but there's a big difference between mentioning a few
confounders and pointing out a major confound that could not just explain the
result entirely but also explain why nutrition results have been and will be
systematically wrong.

