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The issue has become known as the Ferguson effect, named after the St. Louis suburb where a police officer shot and killed an unarmed black teenager in August 2014. The shooting set off protests and riots that summer, and eventually gave way to a fevered national debate over race and policing. Many law enforcement officers have said that the intense focus on policing in the time since has put them on the defensive and hindered their work.

Criminologists are generally skeptical of the Ferguson effect, many arguing that there simply isn’t enough evidence to definitively link spikes in crime to police acting with increased restraint. President Barack Obama and Attorney General Loretta Lynch have also said not enough data exists to draw a clear connection.

In Chicago, which has experienced record numbers of homicides this year, Mayor Rahm Emanuel has blamed the surge in violent crime on officers balking during confrontations, saying they have become “fetal” because they don’t want to be prosecuted or fired for their actions.

Superintendent Johnson stopped short of saying the attack on the officer was an example of the Ferguson effect in action, but said being under a magnifying glass has caused his police to “second-guess” themselves.

According to Johnson, the 43-year-old officer, who has not been identified, was responding to a car crash Wednesday when a 28-year-old man who was involved in the accident struck her in the face, then repeatedly smashed her head against the pavement until she passed out. He said the attack went on for several minutes and that two other officers were injured as they tried to pull the suspect away, the Chicago Sun-Times reported. The suspect was on PCP, he said, and was finally subdued after officers Tasered and pepper sprayed him.