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One of Slate Star Codex's top all-time articles discusses this very issue. Highly recommend: http://slatestarcodex.com/2014/04/28/the-control-group-is-out-of-co

• jnordwick 9y ago
  > On the meta-level, you’re studying some phenomenon and you get some positive findings. That doesn’t tell you much until you take some other researchers who are studying a phenomenon you know doesn’t exist – but which they themselves believe in – and see how many of them get positive findings. That number tells you how many studies will discover positive results whether the phenomenon is real or not. Unless studies of the real phenomenon do significantly better than studies of the placebo phenomenon, you haven’t found anything. This is such an astute observation that reproduction studies can be used to find a placebo control group for bad scuence. Parapsychology was one such group, but now we can find many others. Brilliant.