http://knowthefacts.uchicago.edu/
eligible voters are
"All graduate students in the School of Divinity, School of Social Service Administration, Division of the Social Sciences, Division of the Humanities, Division of the Biological Sciences, and Division of the Physical Sciences who are or were compensated as full-time and regular part-time teaching assistants, research assistants, course assistants, workshop coordinators, writing interns, preceptors, language assistants, instructors, lecturers, lectors, and teaching interns, in at least one quarter of Autumn 2016, Winter 2017, Spring 2017, Summer 2017, or Autumn 2017, and who have not yet attained their degree or otherwise completed their course of study."
Some wikipedia resulted in 600 (law)+ 400 ( medschool)+ 3140 (business)+noise term ~5000 grad students. I bet the rest of the gap is just low turnout
Some wikipedia resulted in 600 (law)+ 400 ( medschool)+ 3140 (business)+noise term ~5000 grad students. I bet the rest of the gap is just low turnout