The answer to your first question will be subject to some bias. SDN seems to be extreme on both ends. You'll read about a lot of people who have enviable stats and a lot of people who are wondering what their chances are with stats that leave a lot to be desired. I believe that a score of 17 signifies average performance on a national basis. I would go so far as to say the average matriculating score is somewhere around 18-19. http://www.ada.org/sections/educationAndCareers/pdfs/dat_examinee_guide.pdf