I'm sure that someone else has pointed this out, but if someone prevents it from becoming a "mass shooting" then the data set doesn't tell us what you seem to think it does. They aren't mass shootings *because* someone with a firearm prevented them from becoming one. Here's a site with a short list
of potential mass shootings prevented by the use of a firearm.
The article is clear about its criteria and why it selected them. Most accounts of "stopped a mass shooter" I've seen rely on very circumstantial evidence that the a "mass shooting" was in fact stopped.
That's meaningless though. It only becomes a "mass shooting" if it *isn't* stopped. I think it's quite reasonable to assume that if even a single member of the school staff at Sandy Hook Elementary had been armed, that at least some lives would have been saved, and quite possibly most or all of the children given the order of events.
Often they are something like "Shooter shot two people and was then shot leaving the location when he might have gone on to kill more people". Or the shooter had a direct group of targets (revenge, etc) and was killed after the direct altercation with them when there is no indication that the shooter intended to start killing random people.
Except for the cases which don't. Not all shootings are identical Joph. You're contriving reasons why someone with a firearm will magically be less able to prevent a mass shooting than someone without. So teachers dying while vainly trying to shield children with their bodies is heroic and reasonable to accept, but the same teachers would never have the courage to shoot the armed assailant? That seems a bit unlikely to me.
Also, quite a few of the items off that list involve off-duty or former law enforcement. At least a third; I didn't read the linked articles to every one and some don't mention on your collected page that the CCW person was law enforcement.
Are you aware of how many off duty/former law enforcement and military there are running around our country? I'm not sure how this magically becomes a negative. At best, you make a great case for further loosening restrictions on CCW permits. You get that you're basically arguing that it wouldn't be effective because not enough people have them, right?
The supposed correlation in the second article is a joke. The guy shot up the WI temple because of its cultural implications, not because he thought "Sikh temples don't have guns!"
So? Correlations need not be 100% to have value.
This last guy had a connection to the school and likely went there because it was filled with children.
So? Doesn't change the fact that if schools were not gun-free zones, someone might have been there to stop him before he killed 20 kids.
We don't know why the CO shooter picked that specific theater.
And yet, he also followed the same pattern that the author was talking about. Is it perfect? No. Is it a worthwhile correlation to point out and maybe take into account? Absolutely.
I'll point out again though that a shooting event only becomes a "mass shooting" if the shooter intends it to be a mass shooting and no one stops them. There's a massive selection bias in your position because we only label something a mass shooting based on the number of people actually shot and killed. We are thus automatically excluding all cases where someone spotted a potential mass shooting and interrupted it before it became a mass shooting in the first place. We're also only seeing the locations where mass shootings actually occur, and not all the locations they might have occurred at if conditions had been different. If every single school had several staff members who had weapons on campus, might someone who wanted to kill a lot of children avoid going to a school to do so? Might that person even decide on a different type of target, or even a different act in order to make his violent statement?
We can't know for sure all the possible alternatives which might happen. But we can say that right now we've made schools incredibly easy targets for people who decide to use a mass shooting to make some kind of statement. And that's the point being made by this.