I want to do this study sometime. Not because I'm particularly interested in issues of race, crime, or any of that jazz, but because political correctness will bear down on the results with the fervor of 300 angry Spartans. I would like to feel that.
It began when I was reading about average prison IQ in general - it appears to going down. This makes sense - 50 years ago most people could find a menial yet somewhat supportive job. Chalk it up to collective laziness or globalization or the destruction of unions or whatever, but that's no longer the case.
When most people could be reasonably expected of being capable of providing for themselves, the prison population would be driven by what we consider "bad people." Those that commit crimes because they get thrills out of stealing, don't value human life, or can't control their addictions. Those people still end up in jail, but the economic realities of 21st century America mean more and more people are left behind. And there's a pretty stark correlation between intelligence and ability to provide for yourself. So low IQ citizens go without, and the likelihood of committing crime (either out of frustration or as a means to supplement income) goes up. And thus, average prison IQ goes down.
I haven't come across the empirical study backing this up, but that logic is pretty unassailable. However, that's not what I want to study. Looking at prison populations, the racial make up is well known. A significantly greater proportion of the black community is locked up than the white community. And we're not arguing causes (environment, opportunity, culture, institutional racism, poverty all play roles to some degree). I want to look at whether the average black inmate is more intelligent than the average white inmate.
The thinking goes like this: whites, on average, have more opportunities than blacks. They, on average, go to better schools, come from homes with more money, are subject to more constructive expectations, and are more likely to have two-parent homes. Therefore, we expect the next generation to hold better jobs. On average, the whites that don't succeed are more likely to fail due to low IQ (and thus lack of use to society) than a black peer due to the issues discussed above. Painting an example: a white citizen with an IQ of 100 holds the same likelihood of achievement as a black citizen with an IQ of 105 (I'm just picking numbers out of the air here) due to those embedded obstacles.
Let's say the level of achievement hypothesized above is a job with a working wage, consumate with the ability to put a serviceable amount of food on the table, rent for a sanitized apartment, and basic health care. It's on the margin, and one IQ point below means that citizen can't lock down a working wage position and is put at a considerably higher likelihood of committing crime. That would mean an IQ of 99 for your Caucasian, and 104 for your African American. Which means whites are more likely to go to jail if they have IQs of 99 and lower. Blacks, with IQs of 104 and lower. Which would create a prison population wherein one race has an appreciatively higher IQ than another.
Other factors go into this, of course. I believe this would be a driver though. I can also never run for public office.