 He later served as the acting director of the National Institute of Justice for 19 months before joining the University of Pennsylvania in August 2014.Ridgeway's research focuses on using statistical techniques to examine aspects of the United States' criminal justice system.These aspects include, but are not limited to, stop-and-frisk in New York City, which, in a 2007 study, he found was racially biased, with blacks and Hispanics being more likely to be frisked, searched, or arrested once stopped (though they were no more likely to be stopped than whites).