Sphericity and repeated-measures ANOVA
Greenhouse-Geisser correction is used when sphericity is violated
The steps for checking the assumption of sphericity in SPSS
2. Drag the cursor over the General Linear Model drop-down menu.
3. Click on Repeated Measures.
4. Type the number of observations of the continuous outcome being collected.
5. Click the Add button.
6. Click the Define button.
7. Click on the first observation of the continuous outcome.
8. Click on the arrow to move the outcome variable into the Within-Subjects Variables: box.
9. Click on the second observation of the continuous outcome.
10. Click on the arrow to move the outcome variable into the Within-Subjects Variables: box.
11. Click on the third observation of the continuous outcome.
12. Click on the arrow to move the outcome variable into the Within-Subjects Variables: box.
13. Click OK.
The steps for interpreting the SPSS output for the assumption of sphericity
If the p-value is LESS THAN .05, then researchers have violated the assumption of sphericity.
If the p-value is MORE THAN .05, then researchers have not violated the assumption of sphericity.
Was the assumption of sphericity met for repeated-measures ANOVA?
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