Page 57 - Quantitative Data Analysis
P. 57
Quantitative Data Analysis
Simply Explained Using SPSS
Effect Sizes
Effect size - the extent to which the intervention has an effect of
separating two populations.
̅ ̅
There are several measures for effect size. The above formula provides
Cohen’s D effect size.
A statistical test reports statistical significance, or the probability that
results are not due to chance, but does not indicate how large an effect is.
The effect size is interpreted like a z-score, how many standard deviations
different is the treatment mean from the control mean.
• Commonly used Cohen’s d effect size magnitudes:
– Small = .2
– Medium = .5
– Large = .8
The Theory and Applications of Statistical Inferences 41
