A University of Wisconsin-Milwaukee study released Friday found Wisconsin has the nation’s highest rate of incarceration among black men, with drug-related charges being a leading offense.

The study from the UWM Employment and Training Institute found the state’s 12.8 percent incarceration rate among black men is well above the 9.7 percent rate in Oklahoma, the next closest state. The national average is 6.7 percent.

In Milwaukee, the study found more than half of black males in their 30s have been incarcerated, as well as half of black males in their 40s. Two-thirds of Milwaukee County’s incarcerated black males were from the six poorest zip codes in Milwaukee, according to the study.

“The prison population in Wisconsin has more than tripled since 1990, fueled by increased government funding for drug enforcement (rather than treatment) and prison construction, three-strike rules, mandatory minimum sentence laws, truth-in sentencing replacing judicial discretion in setting punishments, concentrated policing in minority communities and state incarceration for minor probation and supervision,” the study said.

Because the vast majority of incarcerated black males are of working age, the study said they struggle finding jobs, especially given the recent recession. The study criticized past reports on the state’s skills gap for “largely ignor[ing]” that population.

Mark Mauer, a spokesperson for the Sentencing Project, said the findings could partly be due to involvement in crime, but also because of the effect of law enforcement policies.

“It is certainly a disturbing indication that there is a problem somewhere that the state incarceration rate is so much higher than the rest of the country,” Mauer said.

The study also found 40 percent of incarcerated black males have offenses related to drugs. Out of all Milwaukee County resident imprisonments related to drugs since 1990, 82 percent of offenders have been black males, according to the study.

While the study also found white male driving while intoxicated offenses are higher than among black males, the opposite held true for drug offenses.

Mauer said the study’s findings are part of a nationwide trend of racial disparities in drug incarcerations.

“I think the state should be reviewing its drug sentencing policies,” Mauer said. “The state should be reviewing the degree at which it is able to offer treatment and alternatives rather than incarceration.”

Fred Kessler, D-Milwaukee, said the imprisonment inequality is a result of policies instituted statewide. He said the mandatory minimum requirement in many sentencing cases disproportionately affects black citizens.

He said the problem also stems from the age being lowered for criminal jurisdiction, meaning people can be tried and imprisoned at a younger age.

“We are treating people as adults earlier than other states, and cases that shouldn’t be treated as crimes, but instead as acts of delinquency, goes on someone’s record early and then it has the impact of them getting into subsequent trouble, making them look like a more serious offender than they actually are,” Kessler said.

The study also offered possible improvements the state could make. Among them were a restructuring of sentencing practices, such as mandatory minimum sentence requirements, transitional job programs for people recently released from prison and state aid to driver’s education.