ARMS Week 3

Question 1

ANCOVA

Answer 1

ANOVA with a covariate.
Has at least three variables:
- one continuous dependent variable
- at least one categorical independent variable (factor)
- one continuous covariate -> variable to control for

NB: lines in graph must be parallel due to assumption of homogeneity of regression slopes

Question 2

Steps of interpreting an ANCOVA graph of comparing group means

Answer 2

1. Draw regression lines. If the lines are parallel, continue to step 2.
2. Draw horizontal lines (from the middle of the groups) to compare the means of the DV on the y-as.
3. Draw vertical lines to compare the means on the covariate on the x-as.
4. Determine the overall mean (vertical lines through middle of vertical lines, ignore groups labels)
5. Shift group 1 to center of overall mean line and determine adjusted mean.
6. Do the same for group 2.
7. Compare the adjusted means of both groups.

Question 3

Mauchly’s test for sphericity

Answer 3

Test for homogeneity assumption for ANOVA repeated-measures
- Only with three or more levels
- Not significant = assumption not violated
- Significant? Look at epsilon
- Epsilon: >0.75 = Huyn-feldt correction; <0.75= Greenhouse geisser correction