Section 51 Introduction to Two-Way ANOVA Flashcards
Two-Way ANOVA
TWO-WAY ANOVA (or Two-Factor ANOVA), subjects are CLASSIFIED in TWO WAYS. (Refer to the “ANOVA 2-Way” tab in the “Quant Psych Tools” Spreadsheet.)
- Ex: A random sample of welfare recipients was assigned to a new job-training program. Another random sample was assigned to a conventional job-training program. (Classification #1 is the training program type). Subjects were also classified according to whether or not they had a high school diploma – Classification #2.
MAIN EFFECT is the result of COMPARING ONE of the WAYS in which the SUBJECTS were CLASSIFIED while TEMPORARILY IGNORING the other way in which they were classified.
- The MEANS are DIFFERENT:
- A Difference in the Column Means indicates that there is a MAIN EFFECT due to the Classification represented by the columns.
- A Difference in the Row Means indicates that there is a MAIN EFFECT due to the Classification represented by the Rows.
INTERACTIONS are when the TWO CLASSIFICATIONS interact to create the ultimate outcome.
- i.e. INTERACTIONS are apparent when you cannot give a complete answer about one of the classifications without ALSO referring to the other classification. That’s because there is an interaction between the two that produces the final result.
- Ex: in the Example above, you cannot fully explain how well the two education programs work (program type is a classification) without also talking about the differences in the results of each program depending on whether or not the subject has received their diploma or not (diploma vs no Diploma is the other classification).
NOTE: That any set of groups with multiple classifications could have results ranging anywhere from ZERO MAIN EFFECTS and ZERO INTERACTIONS to MAIN EFFECTS on EVERY classification and INTERACTIONS among every classification.
NOTE: That at this point in the 2-Way ANOVA has not yet rejected the NULL HYPOTHESIS – the Statistical significance has not yet been determined.
