> If you can separate the population into "definitely diabetic", "definitely not diabetic", and "needs more testing" quickly and cheaply, that's a win.
That's the fundamental problem. It turns out with a reasonably accurate test, a low incidence rate, and a large population, the "definitely X" class will be filled with people who aren't actually X. Going back and trying to separate the two ends up costing more and causing more harm to the non-Xs then just waiting until there's a problem. I'd encourage you to take a look at the link I posted since it takes a very clear look at the problem in the context of mammograms and breast cancer.
That's the fundamental problem. It turns out with a reasonably accurate test, a low incidence rate, and a large population, the "definitely X" class will be filled with people who aren't actually X. Going back and trying to separate the two ends up costing more and causing more harm to the non-Xs then just waiting until there's a problem. I'd encourage you to take a look at the link I posted since it takes a very clear look at the problem in the context of mammograms and breast cancer.