THE NUMBERS that drive Philadelphia prison-reform advocate Patricia Vickers on her mission aren't the big abstract ones.

Not 36,000, the shocking recent estimate of young black men in Philadelphia either behind bars or dead before their time.

Not 1,500,000, the national tally of what academics now call "missing black men."

No, the digits that motivate the 66-year-old mom have been pounded with a sharp needle, black ink jabbed into the soft flesh under Vickers' right bicep - 20 digits that mark the birthdays of her four kids as well as her own.

Vickers' stark tattoo serves as the tangible reminder of what's missing from her life . . . her three sons.

It was March 6, 1990, when she sat in a Center City courtroom and heard a judge - future District Attorney Lynne Abraham - say that her son Kerry Marshall would spend the rest of his life in prison, with no chance of parole, for the murder he was convicted of carrying out when he was 17.

Since then, Vickers' eldest son died at age 33 of complications from drug abuse, while her third son is currently imprisoned for what she described as drug-related offenses.

Maybe that's why an April report in the New York Times on "missing black men" - the dearth of young African-American males compared to black females, based on census data - may have shocked its upscale readers but was barely news in places like West Philadelphia. That's where Vickers volunteers with the Human Rights Coalition to advocate for prisoners' rights.

This week, the NAACP is in Philadelphia for its 106th annual National Convention, bringing together 5,000 civil-rights crusaders from around the nation to discuss a diverse range of issues. These include police brutality and criminal-justice reform, topics that have jumped toward the top of the national agenda in the 11 months since a police-involved killing and protests rocked Ferguson, Mo.

But experts say any conversations about race relations in America in 2015 and beyond won't get far without coming to terms with a type of diaspora that is peculiar to the nation's inner cities - a cycle of poverty, violence and drugs that has acted like a neutron bomb to eliminate young men in their late teens, 20s and 30s.

James Peterson, director of Africana studies and associate professor of English at Lehigh Unversity, said mass incarceration policies are the crux of the problem - thanks to the "war on drugs" and what he calls "certain myths that were propagated in the 1970s and '80s about black male criminality."

Only in recent years has our politics started to focus on the fact that America has the world's highest rate of incarceration and that a disproportionately large amount of the inmates are black. A 2013 Pew Research Center study found that black men in the U.S. are six times more likely than white men to be behind bars.

But while the stats have prompted a slow turn toward alternatives to prison, or marijuana decriminalization, experts say the problem of missing black men will be hard to tackle as long as Americans can't agree on the root causes.

Conservative social critics - including the proponents of stricter sentencing laws in the 1980s - say the solution is largely a matter of personal responsibility, that the calamities that befell Vickers' family were the result of poor choices involving drugs or guns. But those in the black community emphasize the lack of blue-collar jobs, crumbling schools and racial profiling.

For her part, Vickers blames what she calls "the whole system" - from the lack of summer camps and after-school programs for urban kids to the for-profit privatization of some prisons.

"I knew all the boys who came to eat dinner at my house and who were friends with my sons, and some of them spent the night . . . all the kids in the neighborhood," she recalled of her time on 55th Street in Southwest Philadelphia during the 1980s.

"Just about every one of them is locked up."

'Surely this is impossible'

The notion of vanished black men is hardly new to the families in urban neighborhoods who live it every day. But the idea's arrival as an academic concept is fairly recent.

University of Texas sociologist Becky Pettit was in the middle of a study of school dropout rates among African-American students when she saw that the numbers just weren't adding up.

"We found more young, black men who dropped out of high school had gone to prison or jail - for a year - than were alive," Pettit wrote in an email interview. "Surely this is impossible [we thought], but it led to a series of other questions to consider how that could be?"

Pettit and a colleague co-wrote a book, Invisible Men: Mass Incarceration and the Myth of Black Progress, that found so many black men had either died young or disappeared into the bowels of the prison system that commonly used national data on dropout rates, voter participation and joblessness was skewed to make it look as if America were making faster social progress than it really was.

"Around the time of Obama's first inauguration - in January 2009 - young black men without a high school diploma were more likely to be in prison or jail than to be employed," Pettit said. "The high school completion rate among black men has seen little improvement since the early 1990s."

This April, a writer for the New York Times' new data-driven section The Upshot used census data to try to quantify the gaps between how many young black men should be living in their communities and how many were actually "missing." It found that black women aged 25 to 54 and not in jail outnumber black men in that category by 1.5 million.

The report also implied a strong correlation between "missing black men" and wider social dysfunction. The community with a sizable black population and the highest rate of young black males behind bars or prematurely dead turned out to be Ferguson, Mo. - the epicenter of unrest in 2014. In raw numbers, Philadelphia's estimated gap of 36,000 is third in the nation, behind the larger cities of New York and Chicago.

Experts say the chasm really began to widen during the 1980s. That's when a surge in abuse of crack cocaine on city streets led to a spike in murder rates and drug overdoses, and when the criminal-justice system across America grew more harshly punitive - with mandatory minimum sentences, so-called "three strikes" rules for repeat offenders, the increase in life-without-parole sentences, even for youthful offenders, billions of dollars in new prison spending and a "war on drugs" by law enforcement.

Here in Pennsylvania, the overall prison population has increased roughly six-fold since the 1980s.

The skyrocketing numbers of people behind bars coincided with the de-industrialization of cities like Philadelphia and the end of good-paying factory jobs that didn't require a diploma. Lehigh's Peterson says the drug war and aggressive arrest policies "was an obscene way to deal with the loss of the industrial era, the loss of jobs." It's also, in his opinion, the spark for a downward spiral in the urban community - that taking away 36,000 potential workers creates a vacuum that leads to even more job loss.

But the more palpable loss, Peterson and other experts agree, may be the impact on social relations: children growing up without a father; low marriage rates; even guys who are less committed to relationships because there are so many more women around in the neighborhood than men.

Where's daddy?

Karen Lee said her son Marc Lee-Purvis' time behind bars - he's had numerous run-ins with law enforcement related to drugs and weapons, and currently has served four years of a 5-to-12-year sentence - have been hardest on Marc's daughter, now 5. She said relatives have told her that her daddy is away at school.

But now that the girl is older, she's starting to ask questions.

"What kind of school?" Karen Lee said her granddaughter now asks her.

Lee, who works closely with Vickers in activist groups like the Human Rights Coalition and Decarcerate PA and wears a T-shirt protesting mass incarceration as "The New Jim Crow," has seen law enforcement from both sides. She worked as a civilian for the Philadelphia police for 21 years, mostly as a stenographer. But her experiences with her son and law enforcement have made her highly distrustful of cops.

She said she's taken her complaints about officers - who she insists came to her home on numerous occasions, sometimes without a warrant - to the U.S. Justice Department and elsewhere, to no avail.

"We're black, we're poor, we have no money and no connections - who cares about us?" she asked.

In the meantime, she says she lost her longtime home in Queen Village because of the legal bills, and now she lives in North Philadelphia. She said she blames the dearth of black men not just on aggressive policing but the lack of jobs. Near her new home on Berks Street, she'll see a gaggle of men clustered in front of a stoop.

"I know they want to work," Lee said. "They'll say, 'Can I wash your car?' "

Wayne Jacobs, who spent nearly half of his 64 years on earth behind bars, mostly for a slew of non-violent offenses related to heroin addiction and other drugs, now tries to help men with criminal records in the daunting task of finding work, through his group X-Offenders for Community Empowerment.

Growing up in North Philadelphia during the 1960s, Jacobs was brought before a judge for the first time when he was just 11, for shining shoes without a permit in the City Hall courtyard. He was in a gang by 16, and dropped out of high school, later earning his degree behind bars. He said he sees the same patterns with youth he works with today, but he also thinks some things are different, including an erosion of respect.

"There was more structure within the community," he said, and it used to be people didn't spend 15 hours a day listening to music "telling a boy to be a gangster." But there also used to be more work - a boy who dropped out of high school would be told to visit an uncle who worked in a factory and could help with a job, options that barely exist today.

Lehigh's Peterson agrees that "you can't throw out personal responsibility" and that young blacks are getting exactly that message in places like church or community groups, but these conversations "don't make sense absent social, economic and cultural context."

Leadership needed

It is only after a generation of billions of dollars spent on prison construction that politicians - even some conservative GOP presidential candidates - are talking about reduced sentences for nonviolent offenders, alternatives to jail, or even relaxing drugs laws such as Philadelphia's recent decriminalization of small amounts of pot.

"There are a number of policy possibilities, but leadership is needed," said Ann Schwartzman, executive director of the Pennsylvania Prison Society.

The society, the nation's oldest prison reform group, would like to see changes in Pennsylvania's rigid life-without-parole regime that makes it second in the nation, behind Florida, with more than 5,000 locked up with little chance of again seeing freedom.

But Schwartzman and other critics also see problems on the front end of the system, including the fact that as many as 75 percent of the roughly 8,000 people in the Philadelphia prison system are awaiting trial, most unable to afford bail. She says that some inmates lose their home during the long wait for trial, and she urged Philadelphia to study alternatives to cash bail that have succeeded in Washington, D.C., and elsewhere.

As the mass incarceration crisis enters its fourth decade, family and community members are increasingly getting involved in protests like Decarcerate PA's recent 10-day march from Philadelphia to Harrisburg. Inside the warm and dimly lit offices of the Human Rights Coalition on the second floor of an activism center on Lancaster Avenue near 41st, Vickers, Lee and their fellow activists deal with a steady flow of letters from inmates complaining of long stretches in solitary confinement or abuse by prison guards.

In a way, activism is one way to fill the void. With their living sons locked up, the two women push for new policies and new ways of thinking. Not long ago, Lee lobbied Philadelphia fire officials on why ex-offenders can't join the fire department.

"I said, 'Do you think a person who's laying up on the third floor dying of asphyxiation cares if the person on the ladder is an ex-murderer or whatever?' " she recalled. "I said, 'What sense does that make?' "

On Twitter: @Will_Bunch