A p-value says whether an effect exists; an effect size says how big it is.
Your browser does not support embedded video. Download the video (MP4).
:::
Everything in the video, ready to copy:
# Effect size: Cohen's d & Hedges' g library(effectsize) # How big is the mpg gap between gearboxes? cohens_d(mpg ~ am, data = mtcars) # Hedges' g - bias-corrected for small samples hedges_g(mpg ~ am, data = mtcars) # Interpret the magnitude interpret_cohens_d(1.48)
Download this R script · ▶ Practice in the playground
When to use it. Report an effect size alongside every p-value. Use Hedges’ g rather than Cohen’s d for small samples, and interpret with care (0.2 small, 0.5 medium, 0.8 large).
Try the Cohen’s d calculator · read Cohen’s d in R.
Next: Multiple Linear Regression →