1. http://nymag.com/daily/intelligencer/2017/01/new-york-city-had-record-low-crime-rate-in-2016.html

2. https://nycdatascience.com/blog/student-works/pressure-cooker-higher-population-densities-increase-crime/

3.  http://www.jstor.org/stable/10.1086/250109?seq=1#page_scan_tab_contents

4.  http://www.motherjones.com/kevin-drum/2013/01/are-big-cities-more-dangerous-small-ones/