[The government] currently catches, at best, 3 percent of marijuana offenders each year (while the feds are responsible for less than 1 percent of those arrests, representing less than 0.03 of all offenders). These numbers are generous, since they assume that data based on self-reports in surveys do not understate the prevalence of marijuana consumption, which they probably do. In any case, it's clear that only a small percentage of people who violate the ban on marijuana are getting arrested, a situation that invites arbitrary enforcement. A report released [Friday] by the Drug Policy Alliance and the California NAACP illustrates that problem, finding that from 2006 to 2008 "police in 25 of California's major cities arrested blacks at four, five, six, seven, and even 12 times the rate of whites." The racial disparities are not explained by differences in drug use, since the government's survey data indicate that "young whites use marijuana at higher rates than young blacks."