The Pervasive Problem With Placebos in Psychology: Why Active Control Groups Are Not Sufficient to Rule Out Placebo Effects
Walter Boot and colleagues argue that causal claims about a psychological intervention need a control group that accounts for improvement from other factors. Active control groups are better than no-contact controls, but isolate the treatment effect only if they match the experimental group's expectations of improvement. The authors argue that almost no psychological interventions do this, a design flaw that potentially undermines any causal inference. They illustrate the problem with video-game training research and note that it also affects studies of mental health, cognition and education. They conclude that measuring expectations and using alternative designs can help.
Walter Boot and colleagues argue that causal claims about a psychological intervention need a control group that accounts for improvement from other factors. Active control groups are better than no-contact controls, but isolate the treatment effect only if they match the experimental group's expectations of improvement. The authors argue that almost no psychological interventions do this, a design flaw that potentially undermines any causal inference. They illustrate the problem with video-game training research and note that it also affects studies of mental health, cognition and education. They conclude that measuring expectations and using alternative designs can help.
Written from the abstract on the Association for Psychological Science journal page, read 2026-10-23.
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Boot, W. R., Simons, D. J., Stothart, C., & Stutts, C. (2013). The pervasive problem with placebos in psychology: Why active control groups are not sufficient to rule out placebo effects. Perspectives on Psychological Science, 8(4), 445-454. doi:10.1177/1745691613491271