It is very hard. I think that to pin the success of a treatment to a specific intervention is hard, mainly because the people we treat will tell you that in life they might be doing yoga, doing exercise, or engaging in spirituality. Many of these interventions have an impact. It is very hard to dissociate them from the outcome.
What we typically do is double-randomized studies, where we divide the population into two. One gets a particular intervention, whereas the other one doesn't get that activity; otherwise, everything remains the same. Based on that, we derive our conclusions as to whether the treatment is effective or not. On an individual level, it is hard to tell, because something else altogether might have helped them.