Dr. Peter McKenna:

The false positive rate is what is usually looked at. It is the positive predictive value. It takes a couple of months because the smear needs to be matched with the histology report on the biopsy. That is easier to do. The laboratories all fall within a fairly narrow parameter in the early to mid-80s. That is acceptable. The false negative will take a long time to come through because there could be a five or six year gap between a negative smear and the diagnosis of an invasive cancer.