I have a slight problem with this article on Magic Mushrooms from Scientific American, or, truth be told, probably with the original piece of research.

If there is a 'special' screening process, please, please elucidate on it. One of the problems with this kind of research is that there is a massive potential for selection bias (hence endogeneity) and therefore whatever you claim to say is almost entirely going to be bull (your point estimates in regressions, t-stats, etc don't mean anything). Why do I say this? Well... the individuals were 'specially screened' they were not selected randomly. Which I would intuit translates as 'volunteers' who fit a 'profile'. What was this process? How were the volunteers found? What are your identifying assumptions?

Picture: aspiring hippies see sign indicating free mushroom taking, said aspirants might have read, say, Aldous Huxley's The Doors of Perception, or maybe heard of Timothy Leary, or something like that. Anyway, it's fairly feasible to me that such individuals could be primed to say "I felt a sense of oneness with the universe."

What I want to know is, if someone who had never heard of oneness, had never considered universal peace, or thought about The Way of Zen would have made such a claim at all. I really, really think this 'special screening process' needs to be highlighted and given more attention than it is in this SciAm article. The 'conclusions' mean absolutely nothing otherwise.

Note, I understand that randomly selecting people in the population and asking them to be part of a test for psilocybin mushrooms is likely to result in you getting a slap in the face from much of middle America, but at least make some attempt to be sure about the
generalizability of your claims.

UPDATE: So I have just read this article from Science Daily and it is far, far better written than the one referred to above from Scientific American. They refer to the sampling practice, to the delineation of best practices argued from the article as well as the requirements for generalizability from the results. Much, much better. Thank you Science Daily.