Bipartisan collaboration and consistent funding of evidence-based reforms helped slash prison populations in five states with dramatically different demographics and political leanings, according to a study by The Sentencing Project.

The results, charted over roughly a decade in Connecticut, Michigan, Mississippi, Rhode Island, and South Carolina, should be a signal to the rest of the country that “substantial reductions” are possible without endangering public safety, the study authors said.

“We now have evidence that substantial reductions in prison populations are possible in red and blue states,” said Marc Mauer, executive director of The Sentencing Project, and one of the authors of the report.

The analysis found reductions ranging from 14 percent in South Carolina to 25 percent in Connecticut over a period starting about 2007 and ending in 2016.

The reductions “produced a cumulative total of 23,646 fewer people in prison with no adverse effects on public safety,” the report said.

That represented a sharp contrast to the national average over the same period. Although inmate populations have begun to decline, the study cited a recent analysis showing that at the current average nationwide rate of change from 2009 to 2016, it would take 75 years to reduce the country’s prison population by half—and while 42 states have experienced declines from their peak prison populations, 20 of these declines are less than 5 percent.

Moreover, eight states are still experiencing rising inmate populations.

The factors responsible for the declines were different in each of the five states, but the authors identified “key strategies and practices” that all of them shared.

They included:

High-profile leadership, bipartisanship, and collaboration among all components of the state justice system;

An ability to apply outside technical assistance and research findings to evidence-based reforms;

Strong community engagement to drive re-entry and community supervision programs;

Reductions in criminal penalties, and the expansion of specialty and alternative courts; and

Incorporation of “dynamic risk and needs assessments” into the sentencing process.

The study made clear that none of these factors alone guaranteed long-term reductions, adding that a sustained effort to reduce the use of prison as primary punishment—often called “decarceration”—required consistent and adequate funding to pay for the reforms.

But the authors said their findings underscored the fact that by developing a “roadmap to decarceration“ attuned to the individual needs and policy preferences of each state, the nation could achieve far greater reductions in mass incarceration than were commonly assumed by most analysts.

All five states were engaged in the Justice Reinvestment Initiative process, spearheaded by the Pew Charitable Trusts and the Council on State Governments, which was designed to respond to the drivers of prison expansion in each state, and to develop strategies for changes in policies and practices.

“Policymakers around the country have much to learn from the population reduction successes of the five states documented in this report, as well as others that have achieved double-digit reductions in recent years,” the report said.

“(It) reinforces the finding that just as prison populations rose during the 1980s and 1990s due to policy choices, so too can they decline as policymakers adopt targeted goals and strategies.”

The other co-authors of the report were Dennis Schrantz, a corrections consultant and the former deputy director of the Michigan Department of Corrections; and Stephen T. DeBor, the senior policy executive in charge of research, planning and automated data systems for the Michigan Department of Corrections.

A complete copy of the study can be downloaded here.