Logical Fallacy Friday: Argument by Anecdote

So, you’re talking with co-workers or friends over a meal one day and all of a sudden, one of them starts explaining why she’s eating bean sprouts covered in whey protein powder with a side of tofu for lunch.  She spouts off a lot of suspect diet-jargon about combining the right kinds  of macronutrients to maximize your metabolism, and she tells you all that she lost a pants size the first day and despite being unable to sleep due to hunger pangs and glucose withdrawal, it’s really working for her and she thinks you all ought to try it too.  You and your fellow listeners start backing away from the Diet Evangelist slowly.  This person is probably delusional, but she is also committing one of the most common argumentative fallacies under the sun:  Argument by Anecdote.  This is where people generalize from their own experience or the experiences of a friend of their cousin or something they got from an email forward, thinking that their experience with something is representative of all experiences with that something.

Argument by Anecdote is so common because it seems to appeal to something very primal in us.  As a 2008 article in Scientific American–which addresses the use of testimonials in medical debates and the marketing of health products–says:

Our brains are belief engines that employ association learning to seek and find patterns. Superstition and belief in magic are millions of years old, whereas science, with its methods of controlling for intervening variables to circumvent false positives, is only a few hundred years old. So it is that any medical huckster promising that A will cure B has only to advertise a handful of successful anecdotes in the form of testimonials.

Recently, I’ve been doing primary research on the rise of the Christian Science movement in the late-nineteenth centuries.  Christian Scientists believe that the body is not actually real, that only spirit exists, therefore disease and injury are only projections of anxiety and unbelief.  They “heal” by praying and arguing with the patient against the belief in the disease or injury.  What’s ironic is that this movement arose almost in tandem with modern scientific medicine.  Mary Baker Eddy was attracting educated middle class followers by the thousands at the same time that scientists were becoming aware of germs and contagion and public health advocates were pushing for sanitation measures in urban areas.  So how did such obvious superstition win out over science in some circles?  Well, Christian Scientists, being educated, literate folk, got into the publishing industry.  They founded the Christian Science Monitor as a secular newspaper, meant to counter the anti-religiosity of the nineteenth century’s mainstream media (yes, the Christian Science Monitor was the nineteenth century version of Fox News).  But they also founded a periodical that published dozens of testimonials about the effectiveness of Christian Science healing.  Eddy and her followers were masters at using the power of narrative to win people over.

Of course, our own lifetimes contain myriad examples.  The Scientific American article cites the kerfuffle over vaccines and autism, in which a group of highly visible parents have insisted that there is a link between the two despite overwhelming scientific evidence to the contrary:

On the one side are scientists who have been unable to find any causal link between the symptoms of autism and the vaccine preservative thimerosal, which in the body breaks down into ethylmercury, the culprit du jour for autism’s cause. On the other side are parents who noticed that shortly after having their children vaccinated autistic symptoms began to appear. These anecdotal associations are so powerful that they cause people to ignore contrary evidence: ethylmercury is expelled from the body quickly (unlike its chemical cousin methylmercury) and therefore cannot accumulate in the brain long enough to cause damage. And in any case, autism continues to be diagnosed in children born after thimerosal was removed from most vaccines in 1999; today trace amounts exist in only a few.

It’s easy to dismiss Christian Scientists and vaccine alarmists as credulous or dumb or even as charlatans themselves, but trust me, you’ve probably done this before.  We all look for ways to put our experience into coherent narratives, narratives that help us make sense of how the world and how our lives work, even if they aren’t generalizable.  And we all experience the urge to evangelize, even when we know we shouldn’t.  That’s a self-protective measure as well, an attempt to justify our own actions and beliefs by encouraging others to go along with them.

But please just let me eat my lunch in peace and shut up about that acai berry crap.