There are a lot of factors that would be difficult to graph.
Someone mentioned the demise of two parent homes, which I think has to be a factor. But what age do you pick to measure that? Does the second parent count if they were in the home until the child was in middle school, or high school, or do they have to be there until the day of the shooting?
Declining church attendance is a potential factor that I see mentioned often. How often does one need to attend in order to count as an attendant? Do they need to do anything to actively participate, or is just occasionally sitting in a pew for an hour good enough?
What about extracurricular activities? Dating status? Physical appearance? Exercise? Hobbies? What kind of movies do they watch, what books do they read, what kind of music do they listen to?
Much of this gets blamed (I think correctly) on bullying. How many times does someone need to be picked on before they are bullied? How do we define "picked on?" More importantly, are we actually willing to look into these factors and make unpopular changes to fix the problem? What if those answers aren't politically correct? I have felt for years that the over policing of school fights is a big factor in this. I didn't make this feeling up, it's based on my own experience of being the new kid in school too many times. Bullies don't stop because you tell a powerless teacher that you are being picked on. They don't stop because you tell an overworked guidance counselor about your feelings. They don't even stop when you ask them nicely. Ideally, the bully will have peers around who disapprove of the behavior, but that happens less often that we all would hope. Win or lose, the next best option, the only other option I am aware of, is to attempt to stop it yourself. I was fortunate enough to go to school in a time where that meant detention or an in school suspension. Now that same behavior results in a kid being handcuffed and put in the back of a police car. It's ridiculous to arrest middle school kids for defending themselves when no one else will. Kids fight, it's a pressure relief valve. We've sealed that pressure valve and now we're looking around at each other with dumbfounded expressions while the pots are exploding.