unpacking a statistic

September 1, 2009

A new study in the Archives of General Psychiatry reports that the percentage of Americans on antidepressants almost doubled from 5.84% in 1996 to 10.12% in 2005. The first thing that probably hits you after reading that is, “Wow, that’s a big jump in ten years.” The next thing might be something like, “I wonder what caused that big of a jump?”

To an educated (but generally ignorant in psychiatry) observer, a few initial explanations seem plausible:
1) The number of depressed people has simply increased, bringing with it the number of people on medication.
2) Cultural acceptance of depression as a legitimate physiological illness has grown, allowing more people to come out into the open and seek treatment they had previously avoided.
3) Our ability to diagnose the illness has improved, allowing us to catch and treat more cases.
4) Our acceptance of (and desire for) drugs to address our problems has increased (to, what many would say — although I’ll withhold judgment — is an unhealthy level).

The authors of the study mainly think it’s 1). In 91/92, the rate of depression in the US was 3.3% and rose to 7.1% in 01/02. This increase in depression itself is an interesting nugget. If fundamentally we think of depression as a physiological disorder, I find it hard to believe that our brain chemistry has really changed that much in ten years. Another explanation is that people are seeking out their doctors more for mental health problems, but then we start spilling into hypothesis 2) and possibly 4).

The authors also suggest an additional hypothesis:

5) Between 1996 and 2005, four new antidepressants (mirtazapine, citalopram, fluvoxamine, and escitalopram) were approved by the FDA for treating depression and anxiety. Furthermore, while the total promotional spending stayed the same, the percentage of that aimed directly at consumers (rather than physicians) increased from 3.3% to 12.0%. So, another explanation of the increase is simply that there are more, and more aggressively marketed drugs out there.

The point I’m trying to make here is that statistics like, “The percentage of Americans using antidepressants doubled between 1996 and 2005.” (from SciAm) and their handling in casual print or conversation often confuse or obfuscate all the issues really at work. Most of us, myself included, don’t put a lot of (or enough) thought into everything going on behind a statistic when we hear or read about them. We’re not critical, skeptical observers, and that’s dangerous.

It’s nice to get out the magnifying glass and do a little digging every once in a while to really understand what all these numbers actually mean.

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