PSY 429 Experimental Psychology
Class Exercise #8
Main Effects and Interactions in a Two-Way Independent-Measures Analysis of Variance
PSY 429 Experimental Psychology
Class Exercise #8
Main Effects and Interactions in a Two-Way Independent-Measures Analysis of Variance
1. What is a main effect?
2. What is an interaction effect?
3. What are the three components of SS-treatment in a two-way analysis of variance?
4. Sketch a graph for each of the following sets of data. Assume Factor A is the number of words in a word list which participants must learn, either 20 words or 40 words in the list. Assume Factor B is the type of words used in the word list, either abstract words (words lacking a physical referent, e.g. include, describe, intend, complex) or concrete words (words in which a physical referent can be imaged, e.g. book, chair, apple, horse).
State whether or not the graph indicates the presence of an interaction between Factors A and B and be complete in your statement of what the graph indicates.
a.
|
B1 |
B2 |
|
|
A1 |
M = 40 |
M = 10 |
|
A2 |
M = 60 |
M = 30 |
b.
|
B1 |
B2 |
|
|
A1 |
M = 20 |
M = 20 |
|
A2 |
M = 10 |
M = 50 |
c.
|
B1 |
B2 |
|
|
A1 |
M = 20 |
M = 20 |
|
A2 |
M = 10 |
M = 10 |
5. The data below are the result of a two-factor experiment comparing the weight loss achieved from two different diet programs (Factor A) for men versus women (Factor B).
|
B1 |
B2 |
|
|
A1 |
M = 10 |
M = 20 |
|
A2 |
M = 20 |
M = 10 |
a. Do the main effects appear significant to you (you do not have to perform an ANOVA) for diet or for gender?
b. Sketch a graph to determine whether an interaction between diet and gender is likely.
c. As a result of what you discovered in doing a and b above, what would you state as your conclusion?
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