That can be found here.
Brief summary: cities have fewer middle-class neighborhoods, many more rich and poor ones.
Most surprising facts (on p. 10): though most cities gained both rich and poor, most cities gained a lot more poor than rich since 1970.
For example, Atlanta experienced a 22% increase in the number of very low income (50% of regional median or less) areas, and only a 9% increase in high income areas (150% or more of regional median). And Atlanta was the most gentrifying city (of twelve listed) in this respect. By contrast, Baltimore experienced a 26% increase in very low income areas, and only a 1% increase in rich areas.
Conclusion: the extent of gentrification is clearly overrated. For every neighborhood that has "flipped" towards wealth, two or more have "flipped" towards poverty.
I realize that these numbers would look a little different if they were calculated only on a 1990-2000 basis (when cities generally did better than in previous decades). Nevertheless, the basic concern underlying complaints about gentrification (that cities are running out of poor neighborhoods) is just rubbish. Most cities have far a more bounteous supply of poor neighborhoods than they did before 1970, let alone before 1950.
