I can understand you desire for statistically valid, well conceived studies that come to an unassailable conclusion. Unfortunately, the data set for survival situations is almost completely anecdotal, with wildly uncontrolled variables, some of which you mention.

Nobody is claiming that mental factors are preeminent,or even the most significant - simply that they are important, in combination with other aspects of the situation, and that there are instances where, carefully analyzed, attitude, etc. seemed to make the difference.

You rightly point out the existence of the "empty set," those people with the right attitude, who were simply overwhelmed by circumstances. The best mental attitude in the world doesn't do you any good if you step off a 300 foot cliff or attempt to cross a raging river.

Of course, with the right attitude, you might have not put yourself in a vulnerable situation in the first place, or extracted yourself once danger was evident, and so forth, on and on.....

I imagine a competent psychologist might be able to devise a study, both ethically and scientifically valid, that might shed some light on this subject, but that is well outside my field. I'll stick to worrying about the quality of the steel in my survival knife, or the three best means of starting a fire.