Chapter 12: Experiments with More than One IV

Question 1

Interaction Effect

Answer 1

Occurs when the effect of one IV depends on the level of another IV
- It is more interesting than the main effect
- An interaction of two independent variables allows researchers to establish whether or not it “depends”

Question 3

Crossover Interaction (it depends)

Answer 3

• It depends “the variable”
• Describe the results with the phrase “it depends”
• The lines cross each other

Example: “The temperature you prefer depends on which food you’re eating”

Question 4

Spreading Interaction (only when)

Answer 4

• Describe the results with the phrase “only when”
• Only works “when”
• Lines are not parallel and they do not cross over each other

Example: My dog sits when I say sit, but only when I’m holding a treat

Question 5

Factorial Design

Answer 5

• Factorial design is done when researchers want to test for interactions
• It is one in which there are two or more independent variables (also referred to as factors)
• Common factorial design, researchers cross the two independent variables; that is, they study each possible combination of the independent variables
• To test whether an independent variable affects different kinds of people or people in different situation, in the same way

To study manipulated variables or participants variables

Question 6

Marginal Means

Answer 6

• Ae the arithmetic means for each level of an independent variable, averaging over levels of the other independent variable
• Look at the marginal means to inspect the main effects in a factorial design and they use statistics to find out whether the difference in the marginal means is statistically significant

Question 7

Main Effects

Answer 7

• The overall effect of one independent variable on the dependent variable, averaging over the levels of the other independent variable
• Sometimes statistical significance tests indicate that a main effect is statistically significant
• The term can be misleading because it seems to suggest that it is the most important effect in a study (it is not)

Question 8

Independent Groups Factorial Designs

Answer 8

• Both independent are studied as independent groups
• A 2x2 independent groups factorial design has four groups/cells
• This is also known as a between subjects factorial design

Question 9

Within Groups Factor

Answer 9

• Both IVs are manipulated within groups
• Only one group of participants in all four groups/cells
• Also called repeated - measures factorial
• Requires fewer participants

Question 10

Mixed Factorial Design

Answer 10

• Only IV is manipulated as independent groups and the other is manipulated within groups
• This design is intermediate between the within groups design and the independent groups design in terms of number of participants

Question 11

Increasing the # of Levels of an IV

Answer 11

• Researchers can add more levels to each independent variable
• When independent variables have more than two levels, researchers can still investigate main effect and interactions by computing the marginal means and seeing whether they are different

Examples:
2x3 factorial design (6 cells/conditions)
- IV1: 2 levels
- IV2: 3 levels

Question 12

Increasing the # of IV

Answer 12

• Researchers find it necessary to have more than two independent variables in a crossed factorial design

Example:
2x2x2 factorial design
- IV1: Phone use (cell phone vs no cell phone)
- IV2: Age (young vs older)
- IV3: Traffic (light traffic vs heavy traffic)
- 3 main effects: Each main effect represents a simple overall difference: the effect of on independent variable, averaged across the other two independent variables
- 3 two - way interactions: Phone use x age interaction, Phone use x traffic interaction, Age x traffic interaction
- 1 three - way interaction
- A three way interaction, if it is significant, means that the two way interaction between two or the independent variables depends on the level of the third independent variable
- Significant three way interaction means that the difference in differences is different
- Easiest to detect by looking at line graphs of the data

Question 13

Idenitifying Factorial Designs in Empirical Journal Articles

Answer 13

• The method section will describe the design of the study.
• Factorial notation: ___ x ____ x ____
• The results section will examine whether the main effects and interactions were significant

Question 14

Idenitifying Factorial Designs in Popular Press Artticles

Answer 14

• Look for “it depends” or “onlt when: to highlight an interaction
• Look for participants variables (e.g., age, gender, ethncicty)