The lack of response has brought be one step closer to believing that ".22s are insuffecient" is just a load of BS. Everyone seems to say that .22's arent good enough but for some reason, they always fail to give examples.
If you are going to base your research and the validity of the results from the responses here and arrive at the conclusion that because you aren't getting definitive answers to the contrary then the .22 is probably sufficient, then you have a poorly designed research plan.
First of all, what do you call "sufficient"? Technically, since most successful firearm use for self defense does not involve pulling the trigger. The mere presence of a firearm and its perceived threat is sufficient for self defense, even when the gun is unloaded. So caliber doesn't matter one iota at this level and this is the most common use of firearms in self defense!
Another group of people are sufficiently stopped by the mere discharge of a weapon, be it as a warning shot or shot that missed. Once again, caliber isn't an issue. The stop was effectively performed. The threat was mitigated, not neutralized, but mitigated.
Next you have people that do get shot with a given caliber that are psychologically stopped by the impact. Either they turn tail or the drop on the spot (even if the wound doesn't physically make this happen). These are usually soft tissue wounds striking non-vital areas with non-critical wounds. Once again, caliber isn't an issue so much of the damage is still psychological, not physiological.
Next is the level of wounding that does cause critical or life threatening damage, but may not bring quick incapacitation. The wounds are such that the person will be incapacitated if given time to bleed out or sepsis to work. It is at this level that the .22 argument are going to start having merit against them. .22s simply don't do as much damage as larger calibers and are more likely to not bring incapacitation quickly.
Last is the immediate incapacitation. You can look to the one-shot stop database for information here, controversial as it may be. Smaller calibers such as the .22 that are often used do not produce the best results. .25 acp is a poor performer as well. Shot placement is going to be critical and even then, .22s don't always perform well...performing worse than larger calibers.
So it is at these last two levels that the issue of .22 effectiveness is truly critical and it is at these two levels that the fewest actual number of events will be occurring. However, these are the most important events when stopping a person is physiologically critical, not just psychologically critical. Given that the .22 only effects a limited amount of damage compared to larger calibers, do you really want to rely on a .22 to actually perform the necessary physiological stop when larger calibers can do it much better (even if their records are far from perfect)?
Then there is the aspect of ignition system. Rimfire is simply not as reliable of an ignition system as centerfire. So when it comes to self defense reliability when you want your gun to discharge, your chances of that not happening are much greater with a rimfire such as a .22 lr.