Basically standardized tests (and GPAs--however corrected) are both good predictors. Depending upon the institution's objectives, other factors may play in as well though they may not correlate that well to GPA in university which may or may not be a good thing depending on your perspective. My personal opinion in that it doesn't really matter past a certain point. (You don't want people to flunk out but the objective isn't really to get good university grades.)