Marc Mauer is a co-author for a new study that says there has been a sharp increase over the past five years in the number of African-American males age 20-29 in jail, on probation or on parole. The study finds, on any given day, one in three black men in their 20s is under some form of court supervision. Five years ago, a similar study found that the percentage at one in four blacks. The study is titled Young Black Americans and the Criminal Justice System: Five Years Later. it's two authors are Marc Mauer and Tracy Huling.