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Area of Science:

  • Exercise Science
  • Biostatistics

Background:

  • Group comparison studies often use within-group effect sizes (e.g., Cohen's d) and percent change to assess intervention efficacy.
  • These traditional methods are susceptible to pre-test variability and baseline values, potentially misrepresenting intervention effects.

Purpose of the Study:

  • To illustrate the misuse of effect size and percent change measures in intervention studies.
  • To highlight appropriate methods for presenting intervention response data.

Main Methods:

  • A realistic sample dataset comparing two resistance training groups with identical pre-test to post-test changes was utilized.
  • Commonly performed statistical tests within the existing literature were computed.

Main Results:

  • Within-group effect size favored the control group, while percent change favored the experimental group, demonstrating conflicting and potentially misleading outcomes.
  • Individual response plots or mean change with 95% confidence intervals offer a more accurate representation of intervention impact.

Conclusions:

  • The study highlights the common misuse of effect size and percent change in intervention research.
  • Investigators are urged to report raw data alongside or instead of these potentially misleading statistics for transparent and accurate reporting.