May 31, 2012


With PSA Testing, The Power Of Anecdote Often Trumps Statistics (RICHARD KNOX, 5/28/12, NPR)

Hal Arkes, a psychology professor at Ohio State University, says Fouts' way of thinking is nearly universal. The power of the anecdote almost always overwhelms statistical analysis, he says.

"Statistics are dry and they're boring and they're hard to understand," Arkes tells Shots. "They don't have the impact of someone standing in front of you telling their heart-rending story. I think this is common to just about everybody."

Arkes says anecdotal thinking "contributes to the widespread gross over-estimation of the benefits of PSA screening." He suggests people do a mental exercise to understand what the numbers are saying about PSA:

Imagine an auditorium filled with 1,000 men who had PSA screening tests and another auditorium with 1,000 men who didn't. That represents the kind of studies the federal task force was relying on.

"Take a look at the men in the two auditoriums, the men in the screened and the men in the not-screened auditorium," Arkes says. "There's just as many men who died of prostate cancer in each auditorium, which leads us to think in the aggregate it didn't do any good."

Arkes breaks it down in the journal Psychological Science.

In each auditorium, there would be eight men who died of prostate cancer. But among the thousand who got PSA tests, there would also be 20 men who were treated for prostate cancers that would never have grown and caused symptoms. And five of these needlessly treated men would have lifelong complications, such as impotence and incontinence.

Posted by at May 31, 2012 8:17 PM

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