The left has been looking for years and years for some kind of evidence they could use as propaganda to attack the human right to defend oneself. The result has been numerous attempts but only this one study they could spin their way.
Here is how it works. You search for databases and if you can’t find a suitable one then you collect your own. Once you have a database you carve it up hundreds of ways till you find some correlation that is significant and supports your view. If you don’t find anything, then you start making more and more complex tests and relationships till you find something. In this study, you can expect they looked at small areas, then counties, then states and regions till they found what they were looking for. They may have carved up the data other ways, too, and controlled for as many variables as necessary to get a significant relationship. One clue is the size of the database, the bigger the more ways you can carve it and control it till it gives you what you want.
If a state has a city and a rural region (IL and NY, for examples), then you can dilute the effect of high murder rate in the city with the very low rate in the rural region. That aids your argument but doesn’t tell you an honest story about gun laws. The laws are similar but the crime stats are greatly different. The law is therefore a weak if not irrelevant influence on the outcome. You will note that the authors could not identify causality—that means the entire study is worthless and merely a novelty. Without causal evidence, no recommendations can be made. That is the most important conclusion you must draw and the touting of the study is, therefore, unquestionably nothing but propaganda.
Cornered 'rats tend to be more aggressive (progressive?).