John Lamberth, in his paper Driving while black: A Statistician proves that prejudice still rules the road (1998) discussed the idea that police officers pulled black drivers more often than white drivers.  In his research based on data from Maryland State police searches he discovered that, “although blacks were searched with greater frequency than whites, drugs were found on approximately twenty-eight percent of blacks stopped, and on approximately twenty-eight percent of whites stopped” (Ramirez 2003).  Some officers may act on what is known as “circumstantial correlation,” the belief that “the likelihood of criminal activity increases when people of color are in certain circumstances” (Ramirez 2003). 

This is similar to the case we discussed in class where “self-fufilling expectations equilibria” exist.  According to Lamberth, there are some officers who search black drivers more frequently than white drivers because they have asymmetric information that black people are more likely to be involved in crime, at least under certain circumstances.  Because they are inclined to believe this, they continue to search drivers of color until their expectations are fulfilled, even though there is little evidence to support their belief.  While comparing people to cars may seem like a stretch, this situation is similar to that in which everyone believes that a car for sale is low quality, so no one will bid a high price for it, and because no one will bid a high price then no good cars go on the market and only low quality cars (lemons) are available for sale.  If some police officers believe that blacks are more likely to be involved in criminal activity, then they will be suspicious even of their interactions with innocent blacks, and so they will likely emphasize the interactions they have had with blacks who actually were found with contraband, which as was demonstrated earlier, is the same percentage as whites who were found with contraband.

 http://www.counterpunch.org/drivingblack.html

For more information see:
Defining racial profiling in a post-September 11 world.
Ramirez, Deborah A.; Hoopes, Jennifer; Quinlan, Tara Lai
Pg. 1195(39) Vol. 40 No. 3 ISSN: 0164-0364
June 22, 2003