Actually, 1, 3, and 4 on the original list seem susceptible to statistics to me. If not by professional organization, then individual therapists should have a sense based in experience. 2 is too subjective.

Researchers could get into it: Do studies of randomly selected clients, give them exit interviews, follow up every six months for the next few years, etc.

This thread has made me realize that one of my No. 1's good points is that she did in fact tell me it was going to hurt pretty early on, second or third session at the latest.