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PART III
Analysis of Variance
Chapter 10 Between-Subjects, One-Way Analysis of Variance
Chapter 11 One-Way, Repeated-Measures ANOVA
Chapter 12 Between-Subjects, Two-Way Analysis of Variance
This section covers a family of tests frequently used in psychology called analysis of variance, abbreviated as ANOVA. ANOVAs are difference tests, like t tests. Like t tests, they take a variety of forms, depending on the groups being studied. But they are unlike t tests in one important way. t tests are limited to a maximum of two samples, so they are great for classic studies that have an experimental group and control group. ANOVA can handle three or more groups. So, for example, it can be used with a study where people with headaches are randomly assigned to receive aspirin, acetaminophen, or ibuprofen to see which medication works most quickly.
ANOVAs can also be used for studies with two or more explanatory variables like the one below, in which right-handed people are tested in a driving simulator to see how which hand they have on the wheel and which eye they have on the road affect performance.
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| Both Eyes Open | Right Eye Covered | Left Eye Covered | |
| Use both hands | 2 eyes, 2 hands | L eye, 2 hands | R eye, 2 hands |
| Use right hand | 2 eyes, R hand | L eye, R hand | R eye, R hand |
| Use left hand | 2 eyes, L hand | L eye, L hand | R eye, L hand |
Analyses of variance allow behavioral scientists to ask, and to answer, complex questions, the type of questions that must be posed to understand something as complex as how humans and animals think, feel, and behave.