Chapter 12
Experiments with 2 or more IVs!
Simple Experiments – 1 IV
* Experiments with 1 IV & 2 levels
* Notetaking (laptop, handwritten) à quiz score
* What if there is a significant t-statistic?
* Experiments with 1 IV & 3 levels
* Level of processing (shallow, moderate, deep) à recall
* What is there is a significant one-way ANOVA?
* What if there is not a significant one-way ANOVA?
Multiple IV’s?
Between
Subjects Designs
ONE IV
Only 2
conditions/levels
of IV
Independent
samples t-test
TWO or more IVs
More than 2
conditions/levels
of IV
Factorial ANOVA
One-Way BS
ANOVA
Example: Experiment with 2 IV’s
* Effect of violent TV (absent, present) AND gender
(male, female) on attitude toward death penalty
* Variables?
1. IV 1: Violent TV Show
2. IV 2: Gender
3. DV: Attitude toward death penalty
* You might be interested in whether the effect of
violent TV is the same for males/females
Terminology …
* Factor = independent variable!
* Factorial design = experimental design with more
than one factor (more than one IV!)
* Factorial notation = how we describe the factorial
design Ex: 2 x 2, 3 x 2, 4 x 2, 2 x 2 x 2
* The number of values = the number of IV’s
* ___’s
* 2 x 2 = 2 IVs
* The numbers themselves = the number of levels in each IV
* Actual values
* 2 x 3 = IV1 has 2 levels, IV2 has 3 levels
Experiment with 2 (or more!) IV’s
* Effect of violent TV (absent, present) AND gender
(male, female) on attitude toward death penalty
* Randomly assigned to violent TV condition
* How would we write this in factorial notation?
* 2 x 2 between-subjects factorial
Factorial Design
Factorial Design
Experiments
* Experiments with 2 independent variables can show:
* 2 main effects – 1 for each of the IV’s
* Effect of one IV (ignoring the effects of all other IVs)
* 1 interaction effect – IV 1 x IV 2
* If sig. interaction, this is the most important effect!
* Tells us how the IVs work together or combine to influence the
DV
* Factorial variations
* Between, within, mixed designs
* Number of levels of IV
* Number of IVs
Example
* Effect of drug type (50mg, placebo) AND gender (male,
female) on pain level
* Variables?
1.
2.
3.
IV 1: Drug type
IV 2: Gender
DV: Pain Level
* You might be interested in whether the effect of drug type
on pain is the same (or different) for males versus females.
If different, then this is an indication you have an
interaction effect
2 x 2 Between-Subjects Design
Female
Placebo
50 mg
DV = Pain Level
What numbers go in the cells?
Male