April 25, 2010 11:40
From the first days of medical school, we're taught to stay away from anecdote. "When you see a patient with symptom x, consider the possibilities carefully, but you'd best ignore what the last patient with the same symptom turned out to have. If you assume this is the same illness, time and again you'll find yourself misled by anecdote."
But fervent beliefs growing out of a singular experience seem to be spreading. Today, more and more people are convinced that Diet A, Pill B, Activity C, or Potion D has transformed their lives, and that their experience must apply equally to everyone else. Aided by the Internet and its electronic relatives, new authorities appear instantaneously, and their convictions spread like wildfire. But recall Virginia Woolf's admonition: "Literature is strewn with the wreckage of those who have minded beyond reason the opinion of others."
Scientific medicine struggles to counteract that phenomenon. But it has its own troubles. It's rare that we really prove cause and effect; penicillin definitely kills certain bacteria, but not many other phenomena are so clear. Relatively new research tools, such as clinical epidemiology, decision analysis, and controlled trials, make us better at estimating probabilities and establishing associations, but quicksand abounds and we keep changing our minds as new data are collected and new analytic tools are applied. So one year Vitamin D's not so important, this year it's vital. One year, freezing stomachs cures ulcers; the next year it kills people. The PSA helped us chart the future, now it breeds chaos, and so on.
So as we confuse people with our flip-flops, what right do we have to decry anecdote? And it's not always so bad. We've learned a lot from close observation of interventions with individuals or small groups of patients. It took just a few to teach us that penicillin cured disastrous infections. Isoniazid transformed tuberculosis. And it was immediately clear that a vaccine could prevent smallpox. Was that not anecdotal medicine?
Not so easy. Americans pay millions for homeopathy: pills soaked in water so dilute it lacks even one molecule of the dead spider that's purported to make it a powerful medicine. And what about the placebo effect: how often does your headache clear before the pill dissolves?
Pretty confusing stuff. No wonder we find a "vaccine war!"