I have some experience in that area. If I'm reading this correctly, they don't know race, only ZIP code. They are extrapolating race from zip code. They also se

I have some experience in that area. If I'm reading this correctly, they don't know race, only ZIP code. They are extrapolating race from zip code. They also seem to be deriving results for extrapolated black/hispanic populations based on using the other populations as a control. Its really just a question of whether their sample sizes are large enough to justify a conclusion about the overall population. They are reporting a 95% confidence interval. Real back-of-the-napkin math (read: don't take this to the bank) would say that a sample size of 9,604 could get you a 95% confidence interval with a 1% margin of error on a population of 100 million. So it seems they are doing ok, but this is not to say there are not a bunch of other possible issues or confounds to consider if someone dug into the study.