1. Experiments: Part 4 Main Effects

2. Overview What is a factorial design? What is a main effect?
How can one determine the number of factors, levels, conditions, and main effects present in a study?
Reminder
Make sure to keep up on the readings
Get going on Paper 2 ASAP

3. Review Factor vs. Level Factor = categorical independent variable
Single-factor designs (previous)
Single-factor, two-level design
Single-factor, multi-level design
Factorial designs (today, next lecture, and Paper 2)
Two-factor design
Multi-factor design
Factor = categorical independent variable
Level = category within a factor
Condition = experimental group or cell

4. Factorial Matrix
Factor 1
Level 1
Level 2

5. Factorial Matrix
Anxiety
Low
High

6. Factorial Matrix
Anxiety
Low
High
4.3
8.2
What is the effect of anxiety (independent variable) upon math test performance (dependent variable)?

7. Factorial Matrix
Factor 1
Level 1 of Factor 1
Level 2 of Factor 1

8. Factorial Matrix Factor 1 Level 1 of Factor 1 Level 2 of Factor 1

9. Factorial Matrix Factor 1 Level 1 of Factor 1 Level 2 of Factor 1
Condition A
Condition B
Level 2 of Factor 2
Condition C
Condition D

10. Factorial Matrix
Anxiety
Low
High
Mortality Salience
Absent
Present

11. Factorial Matrix Anxiety Low High Mortality Salience Absent 5.7 4.3
What are the effects of anxiety and mortality salience on support for cigarette taxes?
Anxiety
Low
High
Mortality Salience
Absent
5.7
4.3
Present
9.2
2.1

12. Factorial Matrix Anxiety Low Medium High Mortality Salience Absent 5.7
What are the effects of anxiety and mortality salience on support for cigarette taxes?
Anxiety
Low
Medium
High
Mortality Salience
Absent
5.7
5.6
4.3
Present
9.2
3.8
2.1

13. Factorial Matrix Mood Low Anxiety Medium Anxiety High Anxiety
What are the effects of mood and mortality salience on support for cigarette taxes?
Mood
Low Anxiety
Medium Anxiety
High Anxiety
High Sadness
Mortality Salience
Absent
5.7
5.6
4.3
5.8
Present (newspaper)
9.2
3.8
2.1
9.1
Present (video)
3.9
2.0
8.7

14. Notation Summarized using numbers
Factor = categorical independent variable
Level = category within a factor
Condition = experimental group or cell
Summarized using numbers
2 x 3
2 x 4 x 8
# of Factors = # of numbers
# of Levels on a factor = numbers themselves
# of Conditions = product of the numbers (do the math)

15. Main Effects
Main effect when a factor (categorical independent variable) has an effect on the outcome (dependent variable)
Significant mean difference across levels of the factor
Can be as many main effects as there are factors
One factor: 0 or 1 main effects
Two factors: 0, 1, or 2 main effects, etc.

16. Factorial Matrix Anxiety Low High Mortality Salience Absent 5.7 4.3
What are the effects of anxiety and mortality salience on support for cigarette taxes?
Anxiety
Low
High
Mortality Salience
Absent
5.7
4.3
5.0
Present
9.2
2.1
7.5
3.2

17. Factorial Matrix How many main effects? Anxiety Low High
What are the effects of anxiety and mortality salience on support for cigarette taxes?
Anxiety
Low
High
Mortality Salience
Absent
5.7
Present

18. Factorial Matrix How many main effects? Anxiety Low High
What are the effects of anxiety and mortality salience on support for cigarette taxes?
Anxiety
Low
High
Mortality Salience
Absent
5.7
5.9
5.8
Present

19. Factorial Matrix How many main effects? Anxiety Low High
What are the effects of anxiety and mortality salience on support for cigarette taxes?
Anxiety
Low
High
Mortality Salience
Absent
7.7
5.9
6.8
Present

20. Factorial Matrix How many main effects? Anxiety Low High
What are the effects of anxiety and mortality salience on support for cigarette taxes?
Anxiety
Low
High
Mortality Salience
Absent
7.7
Present
5.9
6.8

21. Factorial Matrix How many main effects? Anxiety Low High
What are the effects of anxiety and mortality salience on support for cigarette taxes?
Anxiety
Low
High
Mortality Salience
Absent
5.0
3.0
4.0
Present
8.0
6.0
6.5
3.5