Well, obviously we don’t know, but there’s a lot of basis for informed speculation.

* Last month, the Chicago Reporter‘s Megan Cottrell asked whether or not the Plan for Transformation–which I think will be Mayor Daley’s biggest legacy, among many–played a major factor in the ongoing decline of Chicago’s black population, and the numbers she found suggests it has: "About a third, or 31,702 black people who left the city between 2000 and 2009 were from public housing areas."

But of course those are the areas surrounding public housing, not exclusive to public housing. In 1997, Sudhir Venkatesh reported an official population of 12,000 in the Robert Taylor Homes alone, compared to around 25,000 in the 1970s, and that’s before the Plan for Transformation began. In 1991, Alexander Polikoff reported that the CHA had a "resident population" of 145,000; while I had trouble finding statistics for the current CHA population, I did find an MIT report from last year that said "the CHA provides homes in both CHA housing and the private rental market to more than 100,000 people." Adding Section 8 recipients as reported in a 2000 Urban Institute study with non-Section 8 residents reported in the 2000 CHA annual report adds up to about 75,000 residents.

It does seem clear that the destruction of high-density public housing, not just under the Plan for Transformation but also during the Clinton administration, has played a role in the decline of Chicago’s black population. And as the Tribune reported in 2008, the Plan for Transformation had fallen far behind goals, leaving many families in limbo and thus more likely to leave.

* Aside from public housing exclusively, Chicago housing policy (not to mention the general culture) has never been conducive to an economically or physically stable black population, particularly after World War II. As Beryl Satter detailed in her masterful book Family Properties, public policy and personal racism destabilized the nascent black middle class in neighborhoods like Lawndale. I can’t help but think that led to a vast increase in the public housing population, which then began to decline precipitously when both local and national policymakers began to take it apart. And at the same time, Rust Belt industrial manufacturing was in decline, which had been a significant cause of the Great Migration in the first place. Steve Bogira’s recent Reader cover story on segregation provides a good thumbnail history:

Sampson has been studying poverty in Chicago for much of the last two decades. He’s found that in Chicago, poverty, like segregation, persists: neighborhoods that were poor and black in 1970 were generally poor and black in 2000. (From 1970 to 2000, not a single Chicago neighborhood changed from black to white.) The neighborhoods of concentrated poverty are also high in cynicism and distrust, he’s written. In a longitudinal study, Sampson focused on the verbal ability of children growing up in Chicago’s poor black neighborhoods and found "detrimental and long-lasting consequences for black children’s cognitive ability rivaling in magnitude the effects of missing one year of schooling." Verbal ability, he noted, is a "major predictor of life outcomes."

These kinds of deep, neighborhood-based problems, linked inextricably in Chicago to racial segregation, are why desegregation advocates continue to maintain that segregation itself needs to be confronted.

Perhaps the question isn’t "why is Chicago’s black population in decline?" but "why wouldn’t it be?"

* But black flight isn’t solely a Chicago phenomenon. New York’s black population declined as well, while the black populations of major Southern metropolises grew. And as Lee Bey points out, a shrinking city is difficult to manage.

* Speaking of public policy and housing, in an interview with the New York Times‘s David Leonhardt, Harvard economist Edward Glaeser mentions "three big anti-urban policy biases: pro-homeownership policies that push people from urban apartments into suburban homes, the subsidization of transportation infrastructure in low-density areas and our system of local schooling that pushes so many parents away from big-city school districts."

* Aaron Renn, aka the Urbanophile, has a good first reaction to the Census figures at New Geography, in which he discusses black flight not just to the south but the Chicago suburbs and far exurbs; Greg Hinz discusses similar themes.

* And just as a reminder, the city’s housing prices were particularly volatile during the housing bubble.

Update: A new report from the Voorhees Center for Neighborhood and Community Improvement at UIC says that immigrants are increasingly going straight to the suburbs without passing through Chicago first; Progress Illinois explains.