well, there's a bunch of other ways to see this. one is that the problem is that law has been fashioned that disproportionately criminalizes activities that poorer african-american communities would be likely to engage in--such as operating in the informal economies around drugs. there's a ton of sociological data available that correlates imploded infrastructure, lack of conventional economic opportunities etc. with participation in these economies.
another would be to see in these numbers an effect of class in the distribution of access to legal counsel---but on that i don't have information that would let me go too far in correlating convictions rates with reliance on public defenders or self-representation. intuitively it makes sense, but that's it.
or you can see this as part of deliberate choices--cutting back on the redistribution of wealth for social purposes, including the amelioration of class differences---has exacerbated those differences. one index of this is an explosion in the rates of people who are incarcerated. the correlation is that making more rigid existing criminal law and in the fashioning of new laws etc, the prison system has been integrated by the right as a mechanism that allows from management of class tensions--which are exacerbated by their skewed policies that favor military contractor profits and tax breaks for the wealthy while talking some nebulous populist line that keeps the poujadiste voting block in line.
and this is not to even start talking about socio-economic and addiction factors that explain recidivism rates. this is a long-term study by the florida prison administration on these rates. it's kinda depressing...
http://www.dc.state.fl.us/secretary/...ivismStudy.pdf