Looking at the changing demographics of modern mass incarceration

The Marshall Project has this notable new piece headlined "A Mass Incarceration Mystery: Why are black imprisonment rates going down? Four theories." Here is the start of the extended analysis along with the basics of the propounded "four theories":

One of the most damning features of the U.S. criminal justice system is its vast racial inequity. Black people in this country are imprisoned at more than 5 times the rate of whites; one in 10 black children has a parent behind bars, compared with about one in 60 white kids, according to the Stanford Center on Poverty & Inequality.  The crisis has persisted for so long that it has nearly become an accepted norm.

So it may come as a surprise to learn that for the last 15 years, racial disparities in the American prison system have actually been on the decline, according to a Marshall Project analysis of yearly reports by the federal Bureau of Justice Statistics and the FBI’s Uniform Crime Reporting system.  Between 2000 and 2015, the imprisonment rate of black men dropped by more than 24 percent. At the same time, the white male rate increased slightly, the BJS numbers indicate.

Among women, the trend is even more dramatic. From 2000 to 2015, the black female imprisonment rate dropped by nearly 50 percent; during the same period, the white female rate shot upward by 53 percent. As the nonprofit Sentencing Project has pointed out, the racial disparity between black and white women’s incarceration was once 6 to 1. Now it’s 2 to 1.

Similar patterns appear to hold for local jails, although the data are less reliable given the “churn” of inmates into and out of those facilities. Since 2000, the total number of black people in local detention has decreased from 256,300 to 243,400, according to BJS; meanwhile, the number of whites rose from 260,500 to 335,100. The charts below from the Vera Institute of Justicealso reveal significant drops in the jailing of blacks from New York to Los Angeles, coinciding with little change for whites.  (In both the prison and jail data, the total number of incarcerated Latinos has increased, but their actual incarceration rate has remained steady or also fallen, attributable to their increasing numbers in the U.S. population generally.)

Taken together, these statistics change the narrative of mass incarceration, and that may be one reason why the data has been widely overlooked in policy debates. The narrowing of the gap between white and black incarceration rates is “definitely optimistic news," said John Pfaff, a law professor at Fordham University and an expert on trends in prison statistics. "But the racial disparity remains so vast that it’s pretty hard to celebrate.  How exactly do you talk about ‘less horrific?'”

According to Pfaff, “Our inability to explain it suggests how poorly we understand the mechanics behind incarceration in general.”  In other words, how much of any shift in the imprisonment rate can be attributed to changes in demographics, crime rates, policing, prosecutors, sentencing laws and jail admissions versus lengths of stay? And is it even possible to know, empirically, whether specific reforms, such as implicit bias training, are having an effect on the trend line?....

[H]ere are four (not mutually exclusive or exhaustive) theories, compiled from our research and interviews with prison system experts, to explain the nearly two-decades-long narrowing of the racial gap in incarceration.

1) Crime, arrests and incarceration are declining overall....

2) The war on drugs has shifted its focus from crack and marijuana to meth and opioids....

3) White people have also faced declining socioeconomic prospects, leading to more criminal justice involvement....

4) Criminal justice reform has been happening in cities, where more black people live, but not in rural areas....

Even with all of these factors at work, the racial inequity of the American prison system remains vast and continues to wreak devastation on black and Latino communities nationwide. At the current rate, the disparities would not fully disappear for many decades.

I think a lot of other possible factors may be at least marginally contributing to the changing demographics of prison populations between 2000 and 2015, factors ranging from more diversity in the ranks of police, prosecutors and the judiciary to greater concerns with sentencing decision-making (and advocacy) by courts (and lawyers).  And perhaps readers have some additional (sensible?) theories on this front that could be shared in the comments.