Is Prostate Screening Worthless? The Icon Box Speaks
By Bryan Caplan
Gerd Gigerenzer‘s Risk Savvy is strikingly consistent with Hansonian medical skepticism. One striking example: his cost-benefit analysis of prostate screening. His key analytical tool is the icon box.
An icon box brings transparency into health care. It can be used to communicate facts about screening, drugs, or any other treatment. The alternative treatments are placed directly next to each other in columns and both benefits and harms are shown. Most important, no misleading statistics such as survival rates and relative risks are allowed to enter the box. All information is given in plain frequencies.
Here’s what you get if you construct an icon box for prostate screening based on “all medical studies using the best evidence from randomized trials.” Each dot represents 1% of men 50 years and older over the course of ten years.
That’s right. Statistically speaking, prostate cancer screening is worthless. Over the course of ten years, 1-in-100 men dies of prostate cancer regardless of screening. 20-in-100 die for any reason, regardless of screening. The only difference: 2-in-100 screened men – and screened men alone – endure hellish treatments, and another 18-in-100 endure milder torments and a false alarm.
Details on the illusory benefits:
[I]s there any evidence that early detection reduces the number of deaths from prostate cancer? The answer is no: There was no difference… [I]s there evidence that detecting cancer at an early stage reduces the total number of deaths from any cause whatsoever? Again no.
Details on the grotesque costs:
There are two kinds of harms: for men without prostate cancer and for men with prostate cancer that is nonprogressive. When a man without cancer repeatedly has a high PSA level, doctors typically do a biopsy. But unlike a mammogram, a PSA test does not tell the doctor where to inject the needle. As a result, men are often subjected to the nightmare of multiple needle biopsies in search of a tumor that is not there in the first place. These false alarms occur frequently because many men without cancer have high PSA levels…
Men with nonprogressive prostate cancer suffer even more. If a biopsy showed any signs of cancer, most were pushed into unnecessary treatments, such as prostatectomy and radiation therapy… Between 20 and 70 percent of men who had no problems before treatment ended up incontinent or impotent for the rest of their lives.
Gigerenzer actually understates his case. Since 1-in-100 die of prostate cancer either way, we have to conclude that either (a) positive biopsies don’t lead to treatment, or (b) the treatments do not, on average, work. Since (a) is clearly wrong, (b) is the logical inference. If you have terminal prostate cancer, modern medicine won’t help you. It will however still hurt you during treatment, and quite possibly make you incontinent and/or impotent for your remaining years.
When faced with scary medical problems, retreating to “I have to trust my doctor” is very tempting. What Gigerenzer shows, though, is that this trust is misplaced. Relying on doctors is unreliable. Trust transparent statistics instead.