I commend Mr. Ellifritz for taking the initiative and conducting his study to answer his own questions. Yet the conclusions he draws from his study, while sound in the context of the data he used, don't pass the common sense test. If I stand two poor b@stards side by side and shoot them both in precisely the same point in their chest, one with a .25 ACP and the other with a .500 S&W Magnum, I promise you there would be a clear and discernible difference in the effect. Ditto with .25 vs. .45, or .25 vs. .357 Magnum, etc. Suffice to say that the .25 would not seem too impressive anymore.
I suspect that one of the many reasons for the Ellifritz study's strange and counterfactual statistical results is the influence of illegal drugs on the physical response of criminals shot in many of the cases he used as data. I did not see any mention in the article of this variable despite the fact that Ellifritz himself states that "Every shot in this study took place during a military battle or an altercation with a criminal." In other words, the entire study is skewed by a critical variable that Ellifritz overlooked: drugs.
Elsewhere Ellifritz makes some good points -- that often people who are shot just once stop fighting, and that a weapon's rate of fire is often neglected in discussions of "stopping power." Still, I hope that no members here mistake his study for a truly scientific evaluation of the effectiveness of different calibers. According to Ellifritz's wild statistics a .22 round is a more effective single-shot-incapacitator that a .44 Magnum round. If that were true wouldn't most hog hunters choose a .22 over a .44 Magnum?
The last thing I'll point out is that Ellifritz says, in effect, that a "psychological stop" is "adequate" for him when choosing a defensive handgun caliber. I'm happy for him. But personally, I don't carry a handgun to defend myself from the guy who's all bark and no bite. I am crazy enough to carry in preparation for the ULTIMATE CRIMINAL -- someone wearing more than a tank top, with a car door between us, who will not be stopped by a fleshwound and who is, for whatever reason, determined to kill or gravely wound me or a loved one. (I know, what a super-villain!) Psychological stop, really? Best case scenario, it works, and you then get to explain in court why you were justified firing your handgun when all that was required was to convince the guy to leave. I would never, ever, shoot someone to scare them; if I have to fire it will be to *end the threat* because I'm about to be killed. What he terms a "physical stop" is what I call the minimum threshold of effectiveness for my carry handgun. But to each his own, I guess.