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. Author manuscript; available in PMC: 2020 Jun 4.
Published in final edited form as: Eur J Sport Sci. 2019 Jul 9;20(3):326–337. doi: 10.1080/17461391.2019.1632937

Figure 1.

Figure 1.

Distinguishing treatment effects from placebo effects and non-specific effects requires the inclusion of a placebo and no-treatment control group. Panel A shows the observed effect of exercise, which is estimated by comparing the change in the exercise group to the control group. Panel B shows the placebo effect, which is estimated by comparing the change in the placebo group to the control group. Panel C shows that the true effect of exercise can be estimated by subtracting the placebo effect from the observed effect of exercise. In a meta-analysis of nine randomised controlled studies that included an exercise, placebo, and control group, approximately half of the observed effect of exercise on psychological outcomes was attributed to placebo effects (Lindheimer et al., 2015).