African Americans and Latinos are substantially overrepresented among the U.S. prison population, an undeniable legacy of systemic discrimination, historical and contemporary.

These disparities are a major topic in the 2020 presidential campaign, as they should be. “Our criminal justice system cannot be just unless we root out the racial, gender, and income-based disparities in the system,” former vice president Joe Biden’s official campaign website declares, correctly.

What’s also true, though, is that racial and ethnic disparities in incarceration rates are smaller than they were in the recent past, and significantly so. They have, in fact, been decreasing since the 21st century began. The criminal-justice debate needs to catch up with this encouraging trend.

The data appear in a new study from the Council on Criminal Justice, a nonpartisan research organization whose board of trustees includes Black Lives Matter activist DeRay Mckesson, former Obama administration assistant attorney general Sally Yates and Sen. Mike Lee (R-Utah).

According to the study, the ratio of the African American incarceration rate to the white incarceration rate dropped 38.5 percent between 2000, when it was 8.3 to 1, and 2016, when it was 5.1 to 1.

The black-white disparity fell for all categories of crimes, but the largest by far was for drug offenses. In 2000, black people were 15 times more likely than whites to be in prison for dealing or possessing drugs; in 2016, the ratio was just under 5 to 1. (These figures relate to state prisons, which hold the overwhelming majority of all offenders — 1.3 million of nearly 1.5 million in 2017 — but the study’s authors note that disparities are also easing among the 183,000 federal prisoners.)

In that 16-year interval, the number of white men in state prison grew by 59,000 while the number of black men fell by 48,000; the main factor was the 51.4 percent drop in the number of African American men doing time for drug offenses. The number of whites incarcerated for drugs rose by 14.3 percent, meanwhile, possibly a reflection of the opioid addiction epidemic that has hit white-majority rural regions.

Equally striking is the declining disparity between white and Latino incarceration rates. In 2000, Latinos were 2.5 times as likely to be in state prison as whites. In 2016, that ratio was down to 1.5 to 1, a 40 percent reduction.

For both blacks and Latinos, most of the disparity-reduction occurred between 2000 and 2008. In hindsight, the reduction in racially disparate mass incarceration was already underway by 2010, when Michelle Alexander published her agenda-setting book about the issue, “The New Jim Crow.” It also preceded laws to legalize or decriminalize marijuana.

To be clear: A black adult is still five times as likely as a white adult to be in state prison; a Latino adult is still 50 percent more likely than a white counterpart. Those facts should trouble every American.

Nevertheless, U.S. prisons are not filling up with more and more black and brown low-level drug offenders, as much political discourse still implies.

Narratives that blame the 1994 federal crime bill, and its principal Senate sponsor, Biden, for mass incarceration also need updating. A separate Council on Criminal Justice report, published in September, notes that prison population growth in the 1980s and 1990s was mainly due to state sentencing laws that preceded Biden’s bill, and that incarceration actually decelerated after 1994 (though it continued to grow until 2008).

The crime bill’s prison-expansion provisions were never fully funded and probably only increased state prison capacity by 4 percent before lapsing in 2001.

The current discussion could usefully pivot from what went wrong in the 20th century to what’s been going right in the 21st. It’s urgent that policymakers understand the causes of the decline in disparities, with an eye to accelerating it.

In the most basic terms, black people are offending at much lower rates — their reported offending rates declined an average of 3 percent per year between 2000 and 2016 — while the rate for white people increased slightly.

Unpacking the underlying reasons for those trends — the first of which is encouraging, the second of which is not — was unfortunately beyond the scope of the Council on Criminal Justice’s report.

The study does note that racial disparities would have decreased even more if not for the fact that black offenders are still given longer sentences than whites for violent crimes.

Even though drug arrests cause less and less incarceration, expunging minor drug crimes from individual records could help reduce what the study calls “the disparate impact of criminal histories” on sentencing.

Federal, state and local officials will have to dig into such details to make further progress. Fortunately, the data we have already show that progress is possible.

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