Some departments will go decades without an officer firing their weapon....or even pulling it out...lol. Then some, like mine, it's not uncommon. Were those former military drawn to the busier departments who are more likely to use deadly force? Within THOSE departments, were they more likely to fire than the non military...in those departments only? Without that information, the data is worthless.I think you may have a point here.
Those papers listed (which were not peer reviewed as claimed once) tend to look at firing the sidearm in the line of duty as a bad thing. That is a faulty assumption. You have to examine each incident. It might very well be that some incidents needed the sidearm to be fired but the officer failed to do so. This makes not firing the sidearm the bad thing. In such an incident the conclusion would be the opposite of what the paper said. The prior-service candidate would be preferred over the non-service candidate and it would make sense to give preference at hiring.
So by not examining the facts in each incident the authors have rendered any conclusion invalid.