"In 2005, Harvard University and Suffolk University researchers worked with local police to identify 34 "crime hot spots" in Lowell, Massachusetts. In half of the spots, authorities cleared trash, fixed streetlights, enforced building codes, discouraged loiterers, made more misdemeanor arrests, and expanded mental health services and aid for the homeless. In the other half of the identified locations, there was no change to routine police service.
The areas that received additional attention experienced a 20% reduction in calls to the police. The study concluded that cleaning up the physical environment was more effective than misdemeanor arrests."
They probably read your comment as three things instead of two (I did at first and had to take a second look). Tighter binding between the paired items might make it read better, instead of the awkwardly placed comma:
> There is zero relation between filth/crime and living in the city centre.
The areas that received additional attention experienced a 20% reduction in calls to the police. The study concluded that cleaning up the physical environment was more effective than misdemeanor arrests."
https://en.wikipedia.org/wiki/Broken_windows_theory