<<Disclaimer: Verify this information before applying it to your situation.>> Hi All, In discussion with a netfriend, we were considering the analysis posted by a new member to the list, Melissa. I'm afraid I don't remember anything but her first name. Her analysis assumed, if I remember correctly, that the error factor was calculated for the entire group tested. I suspect that it is calculated for the group that demonstrates a positive test result. In a hypothetical construct, if one tests 10,000 healthy people for Ema antibodies, one should get about 40 positives. If the test is 98% specific, then 39.2 should be true positives, and .8 should be false positive. That would mean that in testing 10,000 people, only one should show a false positive. I would welcome further instruction in this area, as I have assiduously avoided statistics in recent years, and am now paying the price. I am not very sure of what I am saying. Best Wishes, Ron Hoggan