Data crunching has been used in policing since the late 1970s. But applying this level of big-data processing — similar to techniques that help determine email spam, a person's movie preferences or advertisements on a social media page — to predict police misconduct is new, experts say. In this foray, data scientists are encountering deep suspicion from officers concerned about the system's fairness and effectiveness. The new approach also raises the complex issue of what to do once the system predicts an officer is likely to misbehave.