It's not surprising that some quasi-standard like ≥4 fatalities would be used as a mass shooting baseline. However, how many details are lost in arriving at whether that "standard" is met and whether the killing was "mass" enough? Why is the number of shooters constrained to one? Wasn't Columbine a 2-shooter event? So, that's not a valid mass shooting?

Also, among the fatalities, when the shooter is included to reach the 4 level, isn't that conflated with a 4-death shooting in which the shooter survives? Isn't the shooter's fate blurred?

Another haunting issue...the number of wounded. If a shooter uses AR-15 NATO ammo, the fatality rates should be higher than with more conventional bullets. Survivability of a hit by a meta-stable .223 round is much less than for many larger, common high-power bullets.

Additionally, how is it that wounded survivors are discounted by the focus on deaths? If the situation allows a shooter to shoot and kill someone with each round, isn't that counted with the situation in which dozens are struck but only 5 die?

There's much more systematic discrepancy to these studies than has been mentioned.