title: The widespread misuse of effect sizes.
abstract: OBJECTIVE
  Studies comparing multiple groups (i.e., experimental and control) often examine the efficacy of an intervention by calculating within group effect sizes using Cohen's d. This method is inappropriate and largely impacted by the pre-test variability as opposed to the variability in the intervention itself. Furthermore, the percentage change is often analyzed, but this is highly impacted by the baseline values and can be potentially misleading. Thus, the objective of this study was to illustrate the common misuse of the effect size and percent change measures.
  
  
  METHODS
  Here we provide a realistic sample data set comparing two resistance training groups with the same pre-test to post-test change.
  
  
  METHODS
  Statistical tests that are commonly performed within the literature were computed.
  
  
  RESULTS
  Analyzing the within group effect size favors the control group, while the percent change favors the experimental group. The most appropriate way to present the data would be to plot the individual responses or, for larger samples, provide the mean change and 95% confidence intervals of the mean change. This details the magnitude and variability within the response to the intervention itself in units that are easily interpretable.
  
  
  CONCLUSIONS
  This manuscript demonstrates the common misuse of the effect size and details the importance for investigators to always report raw values, even when alternative statistics are performed.
authors.affiliation: Department of Health, Exercise Science, and Recreation Management, Kevser Ermin Applied Physiology Laboratory, The University of Mississippi, United States.
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Dankel
authors.affiliation: Department of Health, Exercise Science, and Recreation Management, Kevser Ermin Applied Physiology Laboratory, The University of Mississippi, United States.
authors.forename: J Grant
authors.initials: JG
authors.lastname: Mouser
authors.affiliation: Department of Health, Exercise Science, and Recreation Management, Kevser Ermin Applied Physiology Laboratory, The University of Mississippi, United States.
authors.forename: Kevin T
authors.initials: KT
authors.lastname: Mattocks
authors.affiliation: Department of Health, Exercise Science, and Recreation Management, Kevser Ermin Applied Physiology Laboratory, The University of Mississippi, United States.
authors.forename: Brittany R
authors.initials: BR
authors.lastname: Counts
authors.affiliation: Department of Health, Exercise Science, and Recreation Management, Kevser Ermin Applied Physiology Laboratory, The University of Mississippi, United States.
authors.forename: Matthew B
authors.initials: MB
authors.lastname: Jessee
authors.affiliation: Department of Health, Exercise Science, and Recreation Management, Kevser Ermin Applied Physiology Laboratory, The University of Mississippi, United States.
authors.forename: Samuel L
authors.initials: SL
authors.lastname: Buckner
authors.affiliation: Department of Health, Exercise Science, and Recreation Management, Center for Health Behavior Research, The University of Mississippi, United States.
authors.forename: Paul D
authors.initials: PD
authors.lastname: Loprinzi
authors.affiliation: Department of Health, Exercise Science, and Recreation Management, Kevser Ermin Applied Physiology Laboratory, The University of Mississippi, United States. Electronic address: jploenne@olemiss.edu.
authors.forename: Jeremy P
authors.initials: JP
authors.lastname: Loenneke
mesh_terms: D000704:Analysis of Variance; D016001:Confidence Intervals; D003627:Data Interpretation, Statistical; D006801:Humans; D015233:Models, Statistical; D012107:Research Design; D055070:Resistance Training
keywords: Cohen’s d; Muscle hypertrophy; Muscle size; Percentage change; Statistics