What do false positives and negatives have to do with screening tests for cancer? Elizabeth Tracey reports

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A blood test used for population based cancer screening fell short of allowing cancers to be detected earlier, was cost prohibitive and delayed diagnoses for others, a new study shows. Johns Hopkins Kimmel Cancer Center director William Nelson says both false positive results, where the test shows a cancer is present but it’s not, and false negative results are problematic.

Nelson: Those are the kinds of things that consume resources, particularly false positives. If you have a suspicion of something and then you have to chase it down it consumes resources. If you didn't have a cancer then you wouldn't have been subjected to that. If you had a positive test how sure is it that you actually have a cancer, that's the predictive value. In a resource constrained environment the real premium kind of tests are those that have a high negative predictive value, i.e. you undergo a test that says you don't need to do 10 more things, that you are in fact safe for the time being and you're sure that you're safe.  :34

At Johns Hopkins, I’m Elizabeth Tracey.