Intuitive Biostatistics

The US Preventive Services Task Force has published new guidelines on use of mammograms to detect breast cancer, recommending that they begin at age 50 (rather than 40). Here is a summary in the New York Times, and comments by Matt Briggs (and more). Use this web calculator to play with the numbers. This is a good example to review the concepts of sensitivity and specificity, and false-positive and false-negative test results. This article, written by Dr. Daniel Frank for his patients, does a great job of explaining the big-picture and the concept of Number Needed to Treat (although he never actually uses that term).