Why do you say that?
> Why do you say that?
Because saying the actual figure of 99% will make too many people dismiss the statement as hyperbole /s ...
In all seriousness, we're talking about psychology/psychotherapy here, not psychiatry.
The majority of trials in psychology is characterised by the phrase "non-repeatable", and all the practicing therapies boil down to "this makes a nice narrative".
Using people's self-reported feelings of mental health as an indicator of the efficacy of psychotherapy is no different from asking religious people if prayer helps them and using the answers as proof of the existence of god.
If therapy makes a difference regardless of whether or not the subject believes it does and we can measure that difference then, sure, that's evidence. Until then all we have is "evidence".
Not unrelated, epistemology classes are not mandatory, despite the field being in the rare position of accepting (or at least tolerating) several vastly different epistemological viewpoints. Kind of like studying homeopathy and epidemiology in the same program.