“……Santaella-Tenorio’s study (co-authored with Columbia professors Magdalena Cerdá and Sandro Galea, as well as the University of North Carolina’s Andrés Villaveces) examined roughly 130 studies that had been conducted in 10 different countries. Each of those 130 studies had looked at some specific change in gun laws and its effect on homicide and/or suicide rates. Most of those 130 studies looked at law changes in the developed world, such as the US, Australia, and Austria. A few looked at gun laws in developing countries, specifically Brazil and South Africa.
This isn’t, then, a study that compiled its own original data on one specific gun law. It’s actually more valuable than that: It’s telling us what all the different studies on individual laws say when you examine them put together…….” http://www.vox.com/2016/2/29/11120184/gun-control-study-international-evidence