I'm going to join you down at the bottom here. I agree with you it isn't quite right, and I _think_ the reason comes from a couple sleights of hand. One: healthy people don't go in testing for the presense of a rare disease. That is, if you are administering this test to 10,000 people and only one truly has the disease, then any statistic that you back out of this trial is well below any significance. Two: the colloquial use of 'accuracy' is not the statistical use of 'accuracy'. This post uses the former for our 'intuition' and the latter to demonstrate that our intuition is wrong.