I have recently come across some data that compares the accuracy of two diagnostic tests. We have 214 samples which are tested positive using a "gold standard" test. Using diagnostic test A, 145 / 214 (67.8%) were tested positive, whereas using diagnostic B, 213 / 214 (99.5%) were tested positive. Out of the total of 214, only one sample was tested negative with both test A and B.

We have not used the two diagnostic tests on samples that were tested negative using the "gold standard" test.

I am a bit confused about what is correct statistical test to use here, but decided to vote against the following tests:

- Since both of these two percentages are drawn from the same sample, I cannot use a two-sample t test for percentage (the two samples are not independent of each other).

- I figured that I also cannot use a one-sample t test for percentage because the two percentages were not mutually exclusive of each other (i.e. as they add up to more than 100%).

- I considered using a Chi square test, but I don't think I could form an unbiased "expected" frequency here.

A bit more reading led me to consider the McNemar's test, which (to my understanding) allow repeated testing of the same sample. I put my numbers into GraphPad QuickCalc online and it gave me a p value < 0.0001. I am still unsure if I did the right thing; if anyone could confirm that McNemar's test was the correct test, or if not, suggest a better test to use, I would very very much appreciate it.

Thank you for your time in advance!

Nancy