The screening problem
Nicely summarised by two paragraphs from a story in the Herald
In a separate breast cancer study published online by the British Medical Journal(BMJ), researchers from Norway and the United States found that mammograms carried out once every two years may reduce death risk by about 28 per cent.
About 27 deaths from breast cancer can be avoided for every 10,000 women who did mammography screening – or about one in 368, said the team after analysing data from all women in Norway aged 50 to 79 between 1986 and 2009.
The two prevention numbers — 28% of breast cancer deaths, or one breast cancer death for every 368 women screened — are the same, but they give a very different impression. [Note that this is the age range where mammography works best]
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »