(ABC News on Youtube)
I remember my own natural instincts about cancer screening before a friend in public health set me straight about false positives and other possible harms. I figured the more mammograms I got, the better, right? Same with tests for prostate specific antigen, or PSA, in men, no? The test can save your life. What could be bad?
A lot, of course, including potentially terrible complications from prostate surgery. And earlier this week, a federal panel issued final recommendations against routine prostate screening for healthy men. But the panel’s calculations that the tests do more harm than good have failed to convince many who reason as I used to, that catching cancer early must save lives.
In a paper that couldn’t be timelier, this month the journal Psychological Science publishes an analysis of the “uproar” over prostate screenings last October, when the panel issued its initial recommendations leaning in the same anti-PSA direction.
The Psychological Science paper identifies four psychological factors that “can help explain the furor that followed the release of the task force’s report.” They are:
• The persuasive power of anecdotal (as opposed to statistical) evidence
• The influence of personal experience
• The improper evaluation of data
• The influence of low base rates on the efficacy of screening tests.
The authors, from Ohio State University and The Max Planck Institute for Human Development in Berlin, suggest that the reaction might be different if the panel’s calculations were better explained: “Augmenting statistics with fact boxes or pictographs might help such committees communicate more effectively with the public and with the U.S. Congress.”
I’m all for better explanations. I also can’t help thinking that these psychological factors cannot apply to the experts whose opposition to the anti-PSA recommendations is quoted in this NPR story and in this previous CommonHealth post.
Putting potential arguments aside, the paper offers a wonderfully vivid explanation of public attitudes by presenting the thought experiment of a thousand older men in an auditorium:
Consider two auditoriums, each of which contains 1,000 men age 50 or older. Auditorium “Screened” contains 1,000 men who have had a PSA screening test. Auditorium “Not Screened” contains 1,000 men who have not had such a test. About 8 men from each auditorium will die from prostate cancer in the next 10 years. A very important conclusion to be drawn from these numbers is that screening does not decrease prostate-cancer mortality. How can this be, given that so many men claim to have been saved by a PSA test? Continue reading