The Dunning-Kruger effect, leading to false beliefs about nearly everything since the dawn of humanity.
An economic analyst, Mike “Mish” Shedlock, wrote a blog post to describe how he beat prostate cancer. When laymen and patients write about cancer, they are likely to get some things wrong. Mish’s story is full of typical misunderstandings and misinterpretations.
He interpreted his experience in his own way and did his own research into the medical literature, something he was not qualified to do. Prostate cancer is a very complex subject, and understanding the implications of published studies for treating patients can be difficult even for experts. In typical Dunning-Kruger fashion, he rejected the advice of his doctors, thinking he could do better.
I’m going to follow Mark Crislip’s example and recycle my presentation from The Amazing Meeting last week, not because I’m lazy or short on time (although I am both), but because I think the information is worth sharing with a larger audience.
We’ve all had screening tests and we’re all likely to have more of them, but there is a lot of misinformation and misunderstanding about what screening tests can and can’t do. Screening tests are done on populations of asymptomatic people and must be distinguished from diagnostic tests done on individual patients who have symptoms. Some tests are excellent for diagnostic purposes but are not appropriate for screening purposes.
We’re constantly being admonished to get tested for one thing or another. A typical example was a recent Dear Abby column. She got a letter from a woman who had been screened for kidney disease and learned that she had a mild decrease in kidney function. Abby was shocked to learn that 26 million Americans have chronic kidney disease, and she advised her readers to get their kidneys checked. This was terrible advice. It superficially seems like good advice, because if you have something wrong with your kidneys, you’d want to know about it, right? In fact, if there was anything wrong anywhere in your body, you’d want to know about it. By that logic, it might seem advisable to test everyone for everything. But that would be stupid. It would find lots of false positives, it would create anxiety by picking up harmless variants and anomalies that never would have caused problems, it would be expensive, and it would do more harm than good.
The issue of PSA screening has been in the news lately. For instance, an article in USA Today reported the latest recommendations of the US Preventive Services Task Force (USPSTF): doctors should no longer offer the PSA screening test to healthy men, because the associated risks are greater than the benefits. The story was accurate and explained the reasons for that recommendation. The comments on the article were almost uniformly negative. Readers rejected the scientific evidence and recounted stories of how PSA screening saved their lives.
It’s not surprising that the public fails to understand the issue. It’s complicated and it’s counterintuitive. We know screening detects cancers in an early stage when they are more amenable to treatment. Common sense tells us if there is a cancer present, it’s good to know about it and treat it. Unfortunately, common sense is wrong. Large numbers of men are being harmed by over-diagnosis and unnecessary treatment, and surgery may not offer any advantage over watchful waiting. (more…)
You’ve all heard the dramatic testimonials in the media: “I had a PSA test and they found my prostate cancer early enough to treat it. The test saved my life. You should get tested too.” The subject of screening tests is one that confuses the public. On the surface, it would seem that if you can screen everyone and find abnormalities before they become symptomatic, only good would result. That’s not true. Screening tests do harm as well as good, and we need to carefully consider the trade-offs.
About half of American men over the age of 50 have had a PSA (prostate-specific antigen) screening test for prostate cancer. Recommendations for screening vary. The US Preventive Services Taskforce (USPSTF) says there is insufficient evidence to recommend screening. The American Urological Association and the American Cancer Society recommend screening. Urologists practice what they preach: 95% of male urologists over the age of 50 have been screened. But other groups like the American Academy of Family Physicians recommend discussing the pros and cons of screening with patients and letting them make an informed choice.
Two recent studies published simultaneously in The New England Journal of Medicine have added to the controversy. One concluded that screening does not reduce deaths from prostate cancer; the other concluded that it reduces deaths by 20%. (more…)