Placebo effect for pain
All too often, however, people speak of “the placebo effect” as if it is one effect, equal for all outcomes. This notion is then supported with hand-waving explanations about self-healing. But the research is actually quite clear. There are many placebo effects. Expectation is only one effect among many, and many of these effects are illusory – they create the false appearance of improvement where none exists (like regression to the mean or observational bias). Further, when speaking of the expectation effect we must be careful not to falsely extrapolate this effect from one outcome (like pain) to others.