From the beginning of 2013 to December 2015, San Francisco police officers chose to search black and Latino drivers at much higher rates than whites or Asians after traffic stops, either by invoking probable cause or requesting the driver’s consent. Those searches, however, were much less likely to result in officers uncovering evidence of crimes – potentially signalling bias.

Police say that factors including where they patrol and the demographics of criminal suspects are at the root of those racial disparities, but many social scientists, criminologists and civil rights advocates believe they signal racial profiling. The higher search rates of blacks and Latinos suggest police are more inclined to search drivers of those races, they say, and a lower evidence recovery, or “hit” rate, implies those searches are more often unwarranted.

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