By Stuart Smith
The chance of a mass shooting encouraging a copy-cat attack in the US is 20%-30% and lasts for 13 days. It cannot be known when or why they will attack but once an attack has taken place, the chance of another rises significantly. This is a phenomenon which best seems to be explained using a threshold model with structural determinism, as described by Gladwell.
In the case of a copy-cat attack, there need not be a gradual build-up of pressure over time. They may have all the motivation, weapons and mental instability but require something to tip them over the edge. These will be the people who are hovering just below the threshold, or beginning to move away from it. For the shooter there is no gradual positive feedback making a shooting more and more likely the longer time goes on. What is required is a critical juncture – a trigger. For copy-cat shooters, as the mainstream media love to find and make a deal out of, these are usually examples of long causes with short outcomes.
Once the first shooting takes place, a chain has been set in motion where we do not know when but know that another shooting is far more likely to occur.
What is important here is that the path of a person near the threshold would never necessarily lead to them shooting anyone- they could live their whole lives depressingly close, but never meeting. So their ‘path’ before a shooting was not subject to gradual pressures leading them to an attack. However, there is a possible way path dependent processes could become relevant after the shooting. Once the shooter’s mental state changes, they have a seed in their brain that this kind of action is possible and they may start planning or fantasising their own attack. I can see how negative and positive reinforcement could enter as a major mechanism here.