[aristeides]

Percentage of the population that's black in MD and VA is much higher than that. It's not all that unlikely that a randomly chosen group would be half black. What's really unlikely is the alternation.

[vollmond]

You're right about the population splits. It's roughly 80/20 in Virginia and 70/30 in Maryland instead of the 85/15 I was using. Don't know how Baltimore skews the totals, but it's not that important. Either way, the alternation is unlikely, but not statistically impossible. Having said that, is more likely that it is deliberate selection pattern because there is a human agency involved.