The placebo effect in nutritional supplementation and improvement in performance outcomes : a meta-analysis
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A placebo is an inert substance given to a patient or subject that is not known to cause any physiological benefits. It is used in many clinical trials and research studies, however, there is always the chance the results of the study could display a possible placebo effect. The purpose of this study is to determine if there is a significant placebo effect in respect to nutritional supplements and improvements in strength, endurance, and power. A meta-analysis was used to quantify the size of the placebo effect and to compare a wide variety of supplements and different outcome measures. Effect sizes (ES) were calculated for both post-pre supplementation for within groups (experimental, placebo, and control) and post-supplementation differences between groups. Statistical analysis, including a backward elimination multiple regression was performed on the ES to determine the significance of the difference between groups and which experimental variables were significant predictors of the effect size. The results indicated an ES of 0.06 for post-supplement treatment-placebo, 0.67 post-supplement placebo-control, and 0.98 post-supplement treatment-control. When the effect sizes are directly compared it can be hypothesized that the placebo effect makes up for roughly 70% of the total treatment effect. The results also indicated that other experimental variables may also be important when designing a research study to reduce the chances of displaying a placebo effect. These are: including a treatment, placebo, and control group, double blinding the study, including a familiarization trial, using a moderate training regimen, and untrained individuals.