CH. 12 Factorials Flashcards
What is an interaction effect?
Looking for whether the effect of the original independent variable depends on the level of another independent variable.
Ex. Does the effect of cell phones depend on age?
What is the mathematical way to describe an interaction of two independent variables?
A difference in differences.
The effect of one independent variable depends on the level of the other independent variable
What is a crossover interaction?
“It depends” - ex. People’s preferred food temperature depends on the type of food.
Mathematically: You like ice cream cold more than you like it hot (cold minus hot = positive value) but you like pancakes hot more than you like them cold (hot minus cold = negative value). One value is positive and the other is negative which means crossover interaction.
What is a spreading interaction?
“Only when” - ex. My dog sits when I say “sit”, but only when I’m holding a treat.
Mathematically: When say nothing, there is zero difference between the treat and no-treat conditions (treat minus no treat equals zero). When say “sit” there is a large difference between the treat and no-treat conditions (treat minus no treat equals a positive value). One value is zero and other is value which means spreading.
What is a factorial design?
When there are two or more independent variables (also referred to as factors). In most common factorial design, researchers cross the two independent variables (study each possible combination of the independent variables).
Two-by-two factorial design
Two levels of one independent variable are crossed with two levels of another independent variable. (There are four cells/conditions in this design).
Participant variable
A variable whose levels are selected (ie. measured) not manipulated.
Example: age, gender, ethnicity
If there is no interaction between the independent variables, what will the graph look like?
Parallel lines
Interactions show moderators - why?
In factorial designs, a moderator is an independent variable that changes the relationship between another independent variable and a dependent variable. In other words, a moderator results in an interaction; the effect of one independent variable depends on (is moderated by) the level of another independent variable.
Ex. body weight moderates the effect of alcohol on aggression
What is a main effect?
The overall effect of one independent variable on the dependent variable, averaging over the levels of the other independent variable. In other words, a main effect is a simple difference. In a factorial design with two independent variables, there are two main effects.
How do you calculate a main effect?
- Find marginal means (arithmetic means for each level of an independent variable, averaging over levels of the other independent variable)
- Compare two means, if not large difference there is no main effect, if there is significant difference between the two there is an overall effect for that one independent variable.
Explain why a main effect is sometimes called an overall effect.
The term main effect is usually misleading because it seems to suggest that it is the most important effect in a study. It is not. In fact, when a study’s results show an interaction, the interaction itself is the most important effect. Think of a main effect instead as an overall effect—the overall effect of one independent variable at a time.
Main effects are __________ differences whereas the interaction effect is the ____________ in differences.
simple ; difference
How can you detect an interaction from a table?
- Begin with one level of the first independent variable. Find the difference between the two levels (in one column).
- Find the difference between the two levels of the second independent variable (second column).
- Compare the differences between the two columns. One positive value and one negative value or one zero and one value indicates an interaction. If both values are positive or both values negative, there is no interaction.
How can you detect an interaction from a bar graph?
Draw lines to connect the tops of the bars. If these lines are not parallel, there is likely an interaction.
In a 2x2 independent groups factorial design, how many participants would be needed if the researchers decided to use 50 participants in each cell of the design?
200 (50 in each group - 4 groups/cells)
In a within-groups 2x2 factorial design, how many participants would be needed if researchers wanted 50 participants in each cell?
50 (within-groups means the same participants experience all 4 conditions)
What is a mixed factorial design?
One independent variable is manipulated as
independent-groups and the other is manipulated as within-groups. (see p.371 in text for example)
In a 2 x 3 factorial design, how many independent variables are there, how many levels, and how many cells/conditions?
- 2 independent variables
- IV 1 = 2 levels , IV 2 = 3 levels
- 6 cells/conditions
