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Statistics Resources

This guide contains all of the ASC's statistics resources. If you do not see a topic, suggest it through the suggestion box on the Statistics home page.

Partial Eta Squared

(Partial) Eta Squared

When comparing more than two groups of people, we commonly use eta squared or partial eta squared. In a One-Way ANOVA either value can be reported since they will be the same. With other ANOVA analyses, partial eta squared is more appropriate to report. Partial eta squared is telling us how large of an effect the independent variable(s) had on the dependent variable.

Computing Partial Eta Squared

Starting with computing this value by hand, we can again use a formula. As before, there are several different formulas that can be used. Here is just one example:

where:

  • SS stands for "sum of squares"

In order to complete this computation, you must also know how to compute each sum of squares (deviations from the mean), which can be a time-consuming process, especially with larger data sets. As with the other types of effect size, technology can come to the rescue here.

Partial Eta Squared using SPSS

If you're using SPSS 27 or higher, you can opt to include effect size estimates with your ANOVA analysis. Below are a series of images that show you how to include the effect size estimate with the different types of analyses and where to look in the output to locate the value of the effect size:

1) One-Way ANOVA

one-way ANOVA dialogue window in SPSS

Here is what you will see in the output:

2) Univariate (located under the "Options" menu)

univariate options dialogue window in SPSS

Here is what's included in the output:

tests of between-subjects effects output in SPSS

3) Multivariate (located under the "Options" menu)

view of the multivariate options

Here's how it will appear in the output:

multivariate tests table from SPSS

4) Repeated Measures (located under the "Options" menu)

view of repeated measures options in SPSS

Here is how it will appear in the output:

tests of within-subjects effects table from SPSS

Interpreting the Partial Eta Squared

If no guidelines are provided, you can follow this:

  • η2 = 0.01 indicates a small effect
  • η2 = 0.06 indicates a medium effect
  • η2 = 0.14 indicates a large effect

You'll want to review the guidelines provided in your course materials to confirm as there are differing opinions on the thresholds for each effect level.

 

**For additional assistance with computing and interpreting the effect size for your analysis, attend the SPSS: ANOVA/MANOVA group session**