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Ah, I see what the issue is here. I typically (used to) work in experimental placebo research, rather than clinical placebo research (I'm a psychologist by trade) so I would be more interested in those studies, rather than clinical trials. In terms of what's left over after accounting for no treatment, Vase and H&G got into a big academic fight about this, and it appears that the effect size for placebo effects in pain is approximately (d=0.5), which is a relatively large effect (especially within psychology). This doesn't entirely account for experimenter effects, though with the use of a balanced-placebo design, those can be accounted for. In terms of clinical trials, I would tend to agree with your second definition. Its not perfect, but its as good as it tends to get. I think that one of the issues with placebo research is this notion of mind-over-matter, in that such a viewpoint is the reason that it is perceived as special, and also a reason why people disbelieve in it. Based on old research (Levine, 1979) many (but not all) placebo effects in pain appear to be mediated by endogenous opioids,which I would take to mean that they are pretty naturally mediated by the brain, and so its a physical phenomenon. Many people do go a bit crazy with the woo around it though, I do agree. Funny that this came up today, when I'm currently finalising a hopefully final draft of my thesis on the placebo (PROTIP: never, ever leave your university before submitting a PhD, it tends to go badly). |