Monday, March 30, 2009

bad science of prostate cancer test

In his "Bad Science" column of March 21, Ben Goldacre dissected the reporting of two papers, both published in New England Journal of Medicine, of which one seems to suggest that the PSA (prostata specific antigen) test saves some lives:

European Trial of Prostate-Cancer Screening and Mortality
In this trial, investigators tested the effect of prostate-specific–antigen testing on the death rate from prostate cancer. A significant reduction in prostate-cancer mortality was found after a median follow-up of 9 years.

... while the other suggested it doesn't:

Effect of Screening on U.S. Death Rates from Prostate Cancer
Investigators analyzed the effect of screening with prostate-specific–antigen (PSA) testing and digital rectal examination, as compared with usual care, on the rate of death from prostate cancer. After a follow-up of 7 years, the death rates from prostate cancer did not differ significantly between the two study groups

Goldacre bemoans that papers in the UK only reported the European study which appears to show that the PSA screening is beneficial. What he overlooks in his fury is that there is a very good reason why the studies of the PSA test were reported differently in different countries:

* in the UK, the test is generally not used (my GP very firmly told me that in this country we don't believe in it), hence the first study suggesting that it might save lives counts as newsworthy, while the second study, suggesting that it doesn't, wouldn't be newsworthy.

* in other countries (I know this specifically about Germany), the PSA test is widely used, so the general assumption is that it is useful. In those countries, the study with the positive result would not qualify as news (as it just confirms widely held assumptions) but the study suggesting it doesn't help is important news.

In either case, of course, the non-newsworthy study should have been mentioned along with the newsworthy one. I do, of course, agree with Ben Goldacre's general opinion that science reporting in the mainstream media isn't as good and as clear as it could be. My own recent analysis of how and why science reporting is in decline has appeared here.


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