Five year survival rates can misleadBMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f548 (Published 29 January 2013) Cite this as: BMJ 2013;346:f548
- Gerd Gigerenzer, director, Centre for Adaptive Behaviour and Cognition, Max Planck Institute for Human Development, Berlin,
- Odette Wegwarth, senior research scientist, Harding Centre for Risk Literacy and Centre for Adaptive Behaviour and Cognition, Max Planck Institute for Human Development
While running for president of the United States the former New York mayor Rudy Giuliani announced in a 2007 campaign advertisement, “I had prostate cancer, 5, 6 years ago. My chance of surviving prostate cancer—and thank God, I was cured of it—in the United States? Eighty-two percent. My chance of surviving prostate cancer in England? Only 44 percent under socialized medicine.”1
To Giuliani this meant that he was lucky to be living in New York and not in York, because his chances of surviving prostate cancer seemed to be twice as high in New York. Yet despite this impressive difference in the five year survival rate, the mortality rate was about the same in the US and the UK.
Why is an increase in survival from 44% to 82% not evidence that screening saves lives? For two reasons. The first is lead time bias. Earlier detection implies that the time of diagnosis is earlier; this alone leads …