[matthew3]

Something like the negative effects of concentrated poverty seems to fit Occam's Razor well enough. "The most obviously-shared attribute amongst clusters of extremely poor minorities across the country is the clustering of poverty, and here are some potential causal ways this can lead to different lifestyle habits, different levels of education, different access to health care, etc."

That seems way more likely to me than oft-hinted-at-by-the-"politically-incorrect" "here's a cluster of people who all made the same bad decisions or were victims of the same bad luck in the same way, for no underlying reason other than genetic factors also associated with the color of their skin." That's pretty damn "politically convenient" if you're not in the minority population, too - "hey guys, it's not our fault! They just suck!" Hard to imagine something more politically convenient to the lucky than that.