Definition
Effect size
Effect size is a standardized measure of the magnitude of a difference or relationship — such as Cohen's d or Pearson's r — independent of sample size. It answers 'how big is the effect?' where a p-value only answers 'is it non-zero?'.
Why it matters for HR leaders
L&D and HR programs routinely claim 'statistically significant' improvements that are practically meaningless. Effect size is the honest metric for whether an intervention actually moves the needle.
How Leadify uses it
Leadify reports pre/post effect sizes on capability scores after coaching cycles so L&D leaders can prove ROI in the language finance understands.