Two quick points and I think we can call this thread a wrap.
One, the study is meaningless without an explanation of how they adjusted the data, ie "adjusted incident rate." Off the top of my head, I can't see why you would need to adjust anything, so it sounds like a giant fudge factor which allows them to come up with any answer they want.
Two, even if the statistics are evaluated honestly, which seems highly unlikely, they are useless without some causal link. Otherwise, it is just data mining or, in trader's lingo, curve fitting. It is not immediately apparent why, for example, "universal" background checks would have any discernible impact on "youth" gun deaths. "Universal" background checks refer to a favorite liberal bogeyman, the so-called gun show loophole. Under current law, anyone buying a gun is required to undergo a background check but bona fide private transactions are exempted. Such sales occasionally take place at gun shows, so libs have tried to create a false impression that all gun show sales fly by without background checks. That is demonstrably untrue.
A legitimate study would have linked guns legally acquired without background checks to actual youth homicides. Then there would be at least some cause and effect nexus we could analyze. For example, we know that the disastrous and criminal Obama/Holder Fast and Furious gunrunning op led to the death of a Border Patrol agent. So we can point to that and say there is a clear causal nexus. We can look at the anticipated reward for the operation, eg, a coordinated media campaign to boost anti gun laws, and say that it clearly was not worth the cost.