Lecture on Calculating and Interpreting Eta and Eta Squared using SPSS

Introduction

• Presenter: Dr. Grande
• Topic: Using SPSS to Calculate and Interpret Eta and Eta Squared
• Context: Measure of association for nominal and scale level variables

Data Description

• Variables:
  • Independent Variable: Treatment (Individual, Group, Treatment as Usual)
    • Coded as 0, 1, 2
  • Dependent Variable: Depression
    • Recorded as continuous T-scores (Mean = 50, SD = 10)

Calculating Eta in SPSS

1. Navigate to: Analyze > Descriptive Statistics > Crosstabs
2. Configuration:
   • Move Independent Variable (treatment) to the row list
   • Move Dependent Variable (depression) to the column list
3. Statistics dialog:
   • Under "Nominal by Interval", select Eta
4. Results:
   • Case Processing Summary: 45 observations, no missing values
   • Crosstabulation for treatment and depression shows counts
   • Directional Measures for Eta:
     • Value when depression is the dependent variable: 0.907
   • Interpretation of Eta:
     • Range: 0 (no association) to 1 (perfect association)
     • 0.907 indicates a strong association

Calculating Eta Squared

• Formula: Square the Eta value
  • Example: Eta = 0.907, Eta Squared = 0.907² = 0.823224
• Interpretation: Measures variation explained in the dependent variable by the independent variable

Comparison with Partial Eta Squared

• Definition:
  • Eta Squared: Sum of squares between / Sum of squares total
  • Partial Eta Squared: Sum of squares between / (Sum of squares total + Sum of squares error)
• One-way ANOVA:
  • In one-way ANOVA, Eta Squared = Partial Eta Squared
  • Example: Partial Eta Squared also calculated as 0.823224
• Complex Models:
  • The values differ

Effect Size Interpretation

• Guidelines:
  • Small: 0.02 or 2%
  • Medium: 0.13 or 13%
  • Large: 0.26 or 26%
• Example:
  • Eta Squared = 0.82 or 82% implies a large effect size

Conclusion

• Video aims to help understand calculation and interpretation of Eta and Eta Squared in SPSS
• Questions or concerns can be directed to Dr. Grande for assistance

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