Michigan’s middle 50% range is 28-32. MSU’s is 23-28. According to the 2014 ACT state report only about 8%/9600 of students scored 28 or greater. 26%/31,200 scored 23 or better. That pretty much matches the application numbers, so it seems that it is self-selection. We’d probably get a lot more in-state applicants if we had better public schools.
When loooking at the Naviance profile for my son’s school (a private prep school in Michigan), it seems that MSU has a floor of around 2-9-3.0 GPA. I saw acceptances in that GPA range with ACT’s from 19-30.
Michigan admitted most everyone with a GPA of 3.6 or above and ACT of 26+. Above 3.8, 100% admission. Below that GPA, say at 3.3, you needed to have an ACT of 29 or above. Below 3.2 , only one admittance. (One interesting quirk was that 71% were accepted early, and 63% were accepted regular, much higher for regular that I would have expected. Yield was 38%, about average for Michigan).
The Naviance data seems to indicate that both MSU and Michigan use GPA first, and test scores have less significant impact.