A guard crosses a prison parking lot.
A guard crosses a prison parking lot. Randall Hill/Reuters

A new study from the Vera Institute of Justice says that we should look closely at the populations, and relationship, of local jails and state prisons.

Since 2007, the overall prison population has declined by roughly 1 percent each year. Such a statistic might suggest that the problem of mass incarceration in America is improving. But that belies a complicated truth about the way this nation puts people behind bars.

A new report from the Vera Institute of Justice looks at how incarceration has been measured in the past, and puts forward a new method of evaluation, one that looks at four key indicators: prison admissions, jail admissions, pretrial jail populations, and sentenced jail populations. In order to truly understand the severity and causality of the country’s approach to criminal justice, the report says it is vital to dig into the relationship between local jails and prisons. While federal imprisonment contributes to the issue of mass incarceration, Vera’s study examines local and state incarceration where, they say, data is more readily available and reform efforts are possible more often than they are at the federal level.

Incarceration trends vary widely. While the national prison admissions rate has decreased by 24 percent in the last 12 years, that number has been driven largely by 10 states: California alone accounts for 37 percent of the decline. And trends vary not only from state to state, but also within states themselves. As a result, if people only look at prison data they fail to see what is happening in local jails (jails are usually facilities run by a county or municipality, as opposed to state or federally run prisons, and typically hold people who have been arrested but have not yet been convicted of a crime or sentenced, or who are serving a relatively short sentence).

Much can be hidden when people fail to take variances—state and county, urban and rural—into account. This prompted the researchers to recommend new metrics: jail admissions estimate how much of the local population is affected by incarceration; counting pretrial jail populations helps determine ways in which the bail system is working or failing; tracking the sentenced jail population allows for a more accurate picture of all those serving time, so that people shifted between prisons and jails do not get lost in the shuffle.

Additionally, because most people in prison are serving longer sentences, looking specifically at prison admissions—a number that fluctuates based on changes in legislation or actors in the criminal justice system—is a more responsive metric to measure change than counting the prison population.

Across the country, the state of incarceration is varied and checkered. Some states have seen commensurate movement in stagnation, growth, or decline of both prison and jail populations, while others have seen these populations move in different directions, or at different rates. In Oklahoma, for example, the prison population has been on a slow rise since 2000, but its jail population has nearly doubled.

There are disconnects between the way states and their counties approach incarceration. As an example, the study points to Miami-Dade County in Florida, which has a robust diversion program for those with mental illnesses and substance abuse disorders. In contrast, the state legislature passed a law last year that established mandatory minimum sentences for the possession of fentanyl and its derivatives.

It also highlights New York, Texas, and Missouri, where one of the strongest emerging trends is a decreasing incarceration rate in urban areas that drives down the statewide incarceration average but obscures an uptick in rural areas. And Virginia’s prison admissions have increased by only 4 percent in the last 18 years, but jail admissions in rural areas have increased by 56 percent even as the state’s urban jail population has gone down.

“Some of the problem is just resource scarcity: in smaller places, that looks like criminal justice resource scarcity,” said Jasmine Heiss, Director of Outreach at Vera and an author of the study. “There are fewer diversion programs, [and] finite, small budgets, so there’s not investment in community-based treatment—nothing helping people before they come into contact with the system.”

Because of overcrowding in state prisons, some states have begun playing a kind of shell game: shortening sentences and reclassifying offenses to shift people between prisons and local jails, thereby effectively reducing one population while the the overall footprint of incarceration is unchanged. Not only does this distort the landscape of incarceration data, but it can end up being worse for those caught in the shuffle.

“The worst outcome here is that when more people are held in local jails we find that usually they’re in facilities that don’t have the kind of supports that are needed for people to re-enter well from incarceration,” said Jacob Kang-Brown, one of the study’s authors.  Because jails are primarily built for short-term stays, he said, they usually “lack sufficient recreation space, are often more crowded than prisons, and lack educational or employment opportunities. All kinds of things make jails worse places to do time.”

The metrics Vera suggests are also important because they help to pinpoint specific places in a state for reform targets. While Florida’s prison rate is 13 percent higher than it was in 2000, jail admissions, pretrial detention rates, sentenced jail rates, and prison admission rates, have all gone down. The reason the overall prison incarceration rate is still so high is because the number of people serving 10 or more years in prison doubled in the past two decades, as the system handed down longer sentences.

By only examining prison population data, we risk focusing on a bigger picture that handily obscures pressing points about the state of incarceration in America. “During the rise of mass incarceration, things moved in unison,” said Heiss. “Very few places resisted that rise on the prison and jail level. Now, you have these four different trends.”

“Ultimately,” the report says, “the United States cannot unwind mass incarceration if reformers remain fixated on state-level trends and solutions. The numbers show that ending mass incarceration requires reform everywhere: in states and counties, in prisons and jails.”

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