I know I point to a lot of observational studies. This blogger explains why most of them are wrong.
http://www.medpagetoday.com/GarySchwitzer/31553
As a friend of mine wrote, the rooster crowing in the morning does not make the sun come up, even though a statistical association between the two coinciding is high.
But this is a message about messages -- inaccurate news stories and other messages about observational studies that use causal language where it is inappropriate.
One recent week we saw stories about citrus fruits protecting women from stroke. The very next week it was stories about “sleeping pills could kill 500,000.” And then we also had stories about “omega-3 fatty acids protecting the aging brain“… and about “Vitamin A may slash melanoma risk.” Sometimes it’s stories about lower risk (or protection), sometimes it’s stories about higher risk.
One thing is in common: almost all of the stories are simply wrong, using inaccurate language to describe the kinds of studies in question.
More at the link.
This comic has a good take on correlation vs. causation.
http://xkcd.com/552/
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