Your tax dollars at work.  Statistical inference is not as easy as it looks.
Millions of people reach for an afternoon diet soda as a pick-me-up to make it through the rest of the day. But new research suggests sodas and other sugary drinks — especially artificially sweetened ones — could be related to depression.

According to the research, which will be officially released at the American Academy of Neurology's annual meeting in mid-March, people who drink four cans or more of soda daily are about 30 percent more likely to be diagnosed with depression than people who don't drink soda. Coffee drinkers are about 10 percent less likely to develop depression than people who don't drink coffee.
Without a rigorous causality argument, the researchers' summation is meaningless.
The National Institutes of Health study included more than 250,000 people between the ages of 50 and 71 and studied their drink consumption during 1995 and 1996. A decade later, researchers asked whether participants had been diagnosed with depression since the year 2000.

According to researchers, "the risk appeared to be greater for people who drank diet [rather] than regular soda."
Left unsaid: whether purchasers of diet pop might have been attempting to accomplish on the cheap what a more rigorous regimen of exercise and activity would have produced, and whether the coffee drinkers might have been energizing themselves for more productive activity.  Coffee, after all, is the fuel for theorems.
"Our research suggests that cutting out or down on sweetened diet drinks or replacing them with unsweetened coffee may naturally help lower your depression risk," Honglei Chen, who led the study, said in a statement. "More research is needed to confirm these findings, and people with depression should continue to take depression medications prescribed by their doctors."
That final sentence is a non-sequitur. The diet pop consumption precedes the diagnosis. It's journalistic malpractice to suggest that diagnosed depressives go off their meds and cold turkey on Tab, and pre-depressives who lay off the diet pop might become just as depressed over their adipose tissue as they might be about whatever ultimately gets them diagnosed.

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