I believe the percentiles on the DAT are your percent ranking compared to the all of the nations scores on the test. So if you get like a 90% on an certain test area....you did better than 90% of the people that have taken the test in that section. hope that helps.
I wonder if the percentages are for each individual version of a test compared to other people taking that same version because I also received a 19 on the bio section and my percentile was scaled quite a bit lower than your 91%. Then again, I've heard also that questions are pulled randomly from a large pooled databank which would mean that practically every test is going to be different from the next. Hmmm.
