Here are the waitlist stats for previous two years: Fall 2017, and Fall 2016
http://obp.umich.edu/wp-content/uploads/pubdata/cds/cds_2017-2018_umaa.pdf (page 4)
http://obp.umich.edu/wp-content/uploads/pubdata/cds/cds_2016-2017_umaa.pdf (page 4)
10% (yes, 10%) in 2017-2018 (11,094 - offered, 4109 - accepted to be on waitlist, 468 - admitted).
1% in 2016-2017 (11,197 - offered, 3970 - accepted to be on waitlist, 36 - admitted).
Hope this helps. Son is waitlisted as well.