Their findings manage somehow to be both unsurprising and shocking. In the immediate aftermath of Brown’s death, self-initiated arrests fell 62 percent. Similar declines are seen across nine out of 11 categories of self-initiated activities, including foot patrol (down 82 percent) and pedestrian checks (76 percent). Notably, the decline in arrests is concentrated among misdemeanor arrests (more discretionary than felonies) and among arrests of blacks (rather than whites). This reduction in police activity persisted for at least the next two years. In the same period, the city experienced a significant rise in homicide and aggravated assault.

The multicity analysis shows a similar pattern. Cheng and Long assume that a Ferguson Effect will be more common in cities with higher black population shares, so they compare those in the top quartile of black population against the other cities as a control. They identify the same phenomenon as in St. Louis: the blackest cities saw larger declines in arrests relative to those with smaller black populations, driven by a decline in misdemeanor arrests, and a simultaneous large (10 percent) increase in homicide.