It is not clear how the cities examined by the Times were chosen. The article included ten cities with populations ranging from over 8 million (New York) to just over 317,000 (St. Louis). But there are 60 U.S. cities with estimated 2014 populations in that range. The Times included only four of the 20 most populous U.S. cities. The authors do not explain how those cities were chosen, leaving readers to assume that the findings presented are representative of a broader increase in homicides across U.S. cities. That does not appear to be the case.
Via About Those Rising Murder Rates: Not So Fast @ Marshall Project.