There is always controversy in methodology when studies using field data are involved.
The critics like to nit pick the details and largely miss the point that the goal with a big data study is to find the general performance factors that tend to come out in the wash after all of the uncontrollable variables more or less concrete themselves out.
There can however still be some cartridges with small Ns that have to be considered with an eye to any limits that might come from the small numbers.
There is also a difference between rapid incapacitation, and lethality. I used to know a trauma surgeon from a couple mutual cases. With about 1500 cases under his knife, he felt strongly that the most lethal handgun round was the .230 gr RN .45 ACP. However, there's some experiential bias and some survivorship bias in his observation. As a thoracic surgeon who originally came from South Africa, he had a great deal of experience with people shot with FMJ rounds, and he found .45 ACP was more likely to kill on a shot for shot basis than 9mm or 7.62x25.
In the US, where gun shot victims were often shot with hollow points, the victims had to survive long enough to reach his OR. The fact that he saw fewer hollow point victims, and regarded the .45 ACP FMJ as the most lethal speaks to the potential that people shot multiple times with hollow points didn't live long enough to make it to his OR.
He also commented that the biggest predictor of lethality was number of wound tracts. The more wound tracts, the more organs and systems, compromised and the less likely the damage could be repaired before the victim expired. His view as it didn't matter whether that would track was made with a .22 or a .45.
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When I look at the Ellifritz data or the Marshall answer Sanow data, one of the things I note is the percentage that did not stop. That percentage doesn't get materially smaller with larger or more powerful handgun rounds. Those are the assailants where you have to shoot until they no longer exhibit a threat, even if it's to slide lock.
I also note that even the worst of the one shot stop percentages are usually over 50 percent. That strongly suggests that about half the assailants who are shot are going to stop when shot as they don't wand to get shot anymore. In that half, handgun cartridge doesn't matter.
Handgun cartridge also doesn't matter in the far larger number of handgun self defense uses where the assailant flees before being hit, or flees before the hand gun is even fired, or in some cases before the draw is even complete. Knowing they are about to get shot is enough to end the assault. In those cases the cartridge they are about to get shot with doesn't matter.
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The folks who denigrate the field report data and related studies also seem to forget that the FBIs ballistic gelatin standards were in fact based on the performance in ballistic gelatin of rounds that demonstrated good results in the field.
Bullets are not magically effective because they expand at least 1.5 times their original data and penetrate 12-18". Those performance metrics were adopted because rounds that were effective in the field for the most part and on average also demonstrated that performance in ballistic gelatin.
In that regard the .32 ACP can meet those standards with a 60 gr XTP at 1000-1050 fps, as can the 90 gr XTP in .380 ACP at the same velocities.
But there's also a great deal of value in number of wound tracks and each wound track creates another opportunity for the cardio vascular or CNS hit needed to get rapid incapacitation.
In that regard, a .32 ACP usually offers another round in the magazine in the same model pistol compared to .380 ACP, and it's always lighter recoiling, with the ability for much faster accurate follow up shots.
I regard the two as equal as the extra wound track and ability to deliver rounds accurately on target faster erases any minor advantage the .380 has in wound track diameter.
It was a mainstay in Europe as a law enforcement caliber for over 50 years, and it obviously worked well enough for the job.
), in the same way some people appear to think that having a deadly weapon on their person protects them in some talismanic way. 
