Normality and repeated-measures t-test
Assess normality of difference scores when comparing two observations of a continuous outcome
The steps for conducting skewness and kurtosis statistics on difference scores in SPSS
2. Click Transform.
3. Click Compute Variable.
4. In the Target Variable: box, give the outcome variable a name with a "D" in front of it. Example: "DOutcome"
5. Click on the first observation of the continuous outcome to highlight it.
6. Click on the arrow to bring it into the Numeric Expression: box.
7. Click on the "-" button or simply type "-" in the Numeric Expression: box.
8. Click on the second observation of the continuous outcome to highlight it.
9. Click on the arrow to bring it into the Numeric Expression: box.
10. Click OK.
11. Go to Data View and there is a new variable that contains the difference scores between the two observations of the continuous outcome.
12. Click Analyze.
13. Drag the cursor over the Descriptive Statistics drop-down menu.
14. Select Descriptives.
15. Click on the difference scores variable to highlight it.
16. Click on the arrow to move the variable into the Variable(s): box.
17. Click the Options tab.
18. Deselect Minimum and Maximum boxes under the Dispersion section.
19. Select the Kurtosis and Skewness boxes under the Distribution section.
20. Click Continue.
21. Select the Save standardized values as variables box.
22. Click OK.
The steps for interpreting the SPSS output for skewness and kurtosis statistics
Was the assumption of normality of difference scores met for repeated-measures t-test?
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