The placebo and Hawthorne effects compare and contrast in these ways:
• Both are psychological effects on the participants, causing an effect when the material intervention has no effect.
• Both are effects produced by the participants’ perceptions and reactions; but the former emphasises their response to new equipment or methods, while the latter emphasises their response simply to being studied.
• The leading suspected cause in the placebo effect is the participants’ false belief in the material efficacy of the intervention. The leading suspected cause in the Hawthorne effect is the participants’ response to being studied i.e. to the human attention.
• In both cases, the experimenter may be deceiving the participants, or may be mistakenly sincere, or neutral with respect to the effects of the technology or intervention. In general however, the experimenter appearing to the participant to believe in the efficacy of the intervention, while not essential, may be more, or more often, important to the placebo effect than to the Hawthorne effect.
Related to placebos is evidence about how positive thinking can improve heath outcomes. This area shows that healing and recovery is affected by various kinds of positive thinking. This is not mostly about a placebo effect confounding an experiment, but about better medical outcomes for physically treated patients depending on whether they additionally have positive thinking. The mediating causes are probably: effects on pain; on how well we look after ourselves; and on reduction in persistent stress.