You have to read the previous paragraph to get an idea of the methodology:
Another study...explored relationships between racial bias and political affiliation by analyzing self-reported beliefs, voting patterns and the results of psychological tests that measure implicit attitudes -- subtle stereotypes people hold about various groups.
In other words, if you don't vote like a Democrat, you have a "bias" against blacks.
I had a Lib say to me that I would be so Pro-Life (actually she said anti-choice) if my daughter was raped by a Black guy.
I asked her why she made the rapist Black. Humina humina humina.