It's probably going to be hard to find good data, because the definition of non-traditional can vary a bit. Do you define non-traditional as anyone who doesn't apply directly from undergrad to start medical school without a break in their studies? Because more and more applicants are taking a gap year or two to strengthen their applications before applying. Do you define non-traditional as anyone who had a non-science degree and did a post-bac to pursue medicine? Do you define non-traditional as someone who is a career changer and did something else before applying to medical school?