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... assumption must be that no correlation exists.
No, that's not how statistical tests of significance are interpreted. Failure to reject the null hypothesis does not prove the null hypothesis is true.
http://www.statisticalmisconce...
For example, consider the null hypothesis is "all guns shoot bullets". Then if my test sample happens to contain only bullet-shooting guns, then I cannot reject the hypothesis. But it doesn't prove it either, because my sample may have overlooked legitimate counter examples. Even if the sample was drawn honestly and with no biases. But a single counter-example would be sufficient to disprove the hyposthesis.
Personally, I think the study is flawed because there is no valid control group. I would suggest comparing violence today with 50 years ago.
I grew up in the 50's and 60's. There was a lot less civil violence then. Why is that? There were nothing like "video games" then (except maybe 'cowboys and Indians'). Guns were freely available. In fact much less restricted then now. Movies and TV were much less violent and gory then now. Society had much less civil violence then.
I recall that movies started getting more 'realistic' in the 70's. I remember being at first impressed by the increasingly "realistic" violence portrayed in movies.Up to then it was all theatrics, the good guy shot the bad guy, who clutched his chest and said "you got me" and then slowly slumped over. No blood showing at all usually. Or maybe a little ketchup for 'realism'.
Now I'm no longer impressed with this realism. It sickens me. What have we gained by seeing blood and flesh ripped apart? I think it has made us much less 'emotionally sensitive' to killing. It has never taken much effort to pull a trigger. But there has always been an 'emotional resistance' which traditionally made it difficult to pull the trigger when pointing a gun at a human. That resistance now seems to be wearing off. It's 'easier' now to pull the trigger. Has nothing to do with the design or availability of guns, more with Hollywood and the game industry. IMHO.
Now get off my lawn before I call the cops.