Follow-Up Tests for a Two-Way ANOVA

Question 1

What do you do if you have a significant main effect?

Answer 1

Interpret it to establish the direction of effect
If the factor has more than 2 levels, need to perform a follow-up test to determine which means differ

Question 2

What do you do if you have a significant interaction?

Answer 2

Interpret it to establish the directions of the simple effects

Question 3

What would you do if you have a significant main effect and your factor has more than 2 levels?

Answer 3

Main effect comparisons: Pairwise comparisons (or linear contrasts)

Question 4

What is a protected t-test used for and why is it protected?

Answer 4

It is used to conduct pairwise comparisons (compare 2 means)
It is protected against inflating Type 1 error

Question 5

What is the error term used for pairwise comparisons?

Answer 5

MSerror

Question 6

What are linear contrasts used for?

Answer 6

It is used to determine if a set of groups is different from another set of groups

Question 7

When would you use linear contrasts?

Answer 7

When you have a hypothesis about a set of groups (ie. two levels compared to another two levels)

Question 8

How do you follow up significant interactions?

Answer 8

By conducting tests of the simple effects

Question 9

What do simple effect tests do?

Answer 9

They test the effects of the focal IV at each level of the moderator

Question 10

How do simple effects re-partition variance?

Answer 10

They re-partition the main effect of the focal IV and the interaction variance so that they equal the sum of the simple effects of the focal IV at each level of the other factor

Question 11

How do you follow up a significant simple effect?

Answer 11

If the focal IV has more than 2 levels, a simple comparison must be used to determine where the difference lies

Question 12

What do simple comparisons compare?

Answer 12

They compare cell means using pairwise comparisons