For the first time in a quarter century, the number of African-Americans incarcerated for drug offenses in state prisons has declined more than 20 percent while the number of white imprisoned drug offenders has increased more than 40 percent.

The decline took place over a six year period from 1999 to 2005 and reflects fundamental changes in the so-called "war on drugs" – how it's targeted and prosecuted – as well as the waning of the crack epidemic in predominantly minority urban areas and the increase in methamphetamine abuse in largely white rural neighborhoods.

The trends were identified in an analysis of Justice Department statistics released Tuesday by The Sentencing Project, a criminal justice and reform nonprofit in Washington, D.C. The study found that an increase in the number of drug courts and state-level efforts to find alternatives to incarceration may have played a role in bringing about the change.

"Over the last year or two, largely because of the fiscal crisis, states around the country are reconsidering many of their sentencing and incarceration policies, particularly for lower level drug offenses," says Marc Mauer, executive director of The Sentencing Project and author of the study. "So it seems reasonably likely that we could see some decline in the overall number of people incarcerated for drug offenses."

According to the study, the number of blacks in state prisons on drug-related charges dropped from 144,700 in 1999 to 113,500 in 2005. The number of white drug-offenders in prison increased during the same time from 50,700 to 72,300.

Perceptions of racial bias

When the government ramped up the war on drugs in the 1980s, violent open-air crack markets plagued many urban areas. These areas became the focus of police drug enforcement efforts and crack use invited harsh mandatory minimum sentences.

That led to an exponential increase in the number of imprisoned drug offenders from 40,000 in 1980 to more than 500,000 today, according to Justice Department statistics.

The majority of incarcerated drug offenders have been African-American – despite the fact that drug abuse rates are fairly equal across ethnic and racial lines – and that fed a widespread perception that law enforcement efforts were racially biased.

One impact of the new report, say criminologists, could be that law enforcement will no longer be perceived as biased.

"If citizens believe the criminal justice system is grossly biased, it undermines its effectiveness," says Jonathan Caulkins, a criminologist at Carnegie Mellon University in Pittsburgh.

For years, the disproportionately large percentage of imprisoned African-American drug offenders fueled calls for reform of local police departments as well as the national criminal sentencing structure. Professor Caulkins doesn't want to diminish the presence of racial bias, which he says still exists to some extent in most American institutions, but he contends that incarceration disparities may have had more to do with the nature of the drug epidemic than with overt bias.

In the 1980s, for instance, many urban neighborhoods plagued by the crack epidemic became openly violent. So that's where police targeted their efforts, he says.

"When the sellers are flagrant, then the No. 1 concern is the lack of social order," he says. By contrast, "when the sellers are invisible to the neighbors [as in many affluent white neighborhoods], then you still have the public health problem of addiction and overdose, and that's what you focus on – not law enforcement."

"The difference isn't middle class or poor, white or black, meth or crack," he argues. "The question is: Are the sellers invisible to neighbors?"

Crack dealers who once operated openly on urban street corners have now largely disappeared behind closed doors and disposable cellphone numbers, making them harder for police to track, according to The Sentencing Project report.

Criminal justice reforms a factor?

Other criminologists still see clear racial bias in the way the justice system prosecutes the war on drugs. Apart from the disproportionate incarceration rates, they point to differences in sentencing guidelines for crack cocaine compared with powder cocaine. The two are chemically identical, but the penalties for crack – predominantly used by minorities – remain much harsher than for powder cocaine, which is predominantly used by whites.

The disparity, though, has been reduced in recent years.

That and other reforms of the criminal justice system, such as the development of drug courts in the 1990s which offered treatment in lieu of prison, are also contributing to the decline in the number of African-Americans imprisoned for drug offenses. Mr. Mauer of The Sentencing Project says that's probably because the majority of the more than 2,000 drug courts are located in urban areas.

New York State, which implemented a series of alternatives to incarceration such as drug courts, is a good example of how such policy changes helped lower incarceration rates. In 1999, New York state prisons held about 22,000 people in prison for drug offenses, according to Mauer. By 2005, that had dropped about a third to 14,000.

The state also shows a rise in the number of whites incarcerated for drug offences. In January 2001, whites accounted for 5.4 percent of drug offenders in the New York state prisons. In 2009, that figure had almost doubled to about 10 percent, according to the Correctional Association of New York.

"There have been some modest shifts," says Robert Gangi, of the New York Correctional Association. "But people of color still make up a disproportionately large percentage."

That's led some analysts to argue that the racial shift in national incarceration rates does not reflect changing police and prosecution practices within states so much as the increase in methamphetamine use in many Western and Midwestern states.

"I have no doubt that explains part of the white numbers, because whites are more likely to be arrested for those offenses," says Mauer. "But it's a relatively modest number of states where meth is a problem," he adds.

The question, he says, is whether those meth use numbers are sufficient to explain part or all of the increase in white incarceration rates. "I'm not sure the scale of the change can be explained by that."