Overall, any Ferguson Effect is constrained largely to cities with historically high levels of violence, a large composition of black residents, and socioeconomic disadvantages.Translation: Yes, there has been a Ferguson Effect, most strongly where it would logically occur, in "cities with historically high levels of violence, a large composition of black residents, and socioeconomic disadvantages."
The authors fail to remind us that "high levels of violence, a large composition of black residents, and socioeconomic disadvantages" tend to occur together. It is rare for one (or two) of the three to occur without the others. Hat tip to RealClearPolicy for the link.