Police officers and students exhibit an apparent “hierarchy of bias” in making a split-second decision whether to shoot suspects who appear to be wielding a gun or, alternatively, a benign object like a cell phone, research conducted by the University of Colorado Boulder and San Diego State University has found. Both the police and student subjects were most likely to shoot at blacks, then Hispanics, then whites and finally, in a case of what might be called a positive bias, Asians, researchers found.