I don't know of a controlled study, but doing a study like that is a fine idea. What I know at this point comes from showing this to two groups of depression patients at a hospital here in Boston (about 20 patients in total) and from feedback from some people who tried it on PC (there have also been many thousands of downloads of the notes from all over the world).

Besides SNAP CLUB being an effective treatment for depression, the prediction would also be that the set of symptoms on page 15 of the notes is a sharper indicator of depression than the standard set of symptoms. I would also predict that when SNAPping, fMRIs should show that the dorsolateral prefrontal cortex is activated (the same region targeted by TMS for depression). Practicing SNAP CLUB consistently should show an increased resting activation of the dlPFC and those seeing this effect should get relief from depression. I'm not sure how to quantify it, but the theory also predicts that depression gets worse when things change in your life so that your habitual behaviors no longer work. This would be the explanation for why, for instance, so many people get into trouble when they leave home to go to college or change jobs or cities or careers or partners.

I'm planning on giving a talk to stir up interest here at Boston University, but I'd be happy for anyone to look into this. If you're interested (I notice that you're a medical student in New Zealand), send me a PM.

- vital