The r-squared effect size measure calculator computes the measure (r²) based on the t-score and the degrees of freedom.
INSTRUCTIONS: Enter the following:
r-squared (r²): The calculator returns the effect value as a real number. Note: Small: 0.01-0.09, Medium: 0.09-0.25 and Large: 0.25 and higher.
The r-squared effect size measure, `r^2 = t^2 /(t^2 + df),` is important for determining the size of the difference between the means. It describes what percentage of the data can be explained by the results, or how much of the variability in the data is explained by the independent variable (Gravetter and Wallnau, 2013).
The formula for the r-squared effect size measure is:
r² = t² /(t² + df)
Large: 0.25 and higher
It also lets you specify an alpha level and whether the test is one or two tailed, then it calculates the following results:
The Psychology and Statistics Calculator contains useful tools for Psychology Students. The psychology statistics functions include the following:
Gravetter, F. J., & Wallnau, L. B. (2013). Statistics for the Behavioral Sciences. Wadsworth, CA: Cengage Learning.