COMM 1 Lecture Notes - Lecture 12: Internal Validity, Selection Bias, Random Assignment
23 May 2020
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Investigate the effects of two or more ivs simultaneously. Factorial designs test for two kinds of effects: main effect of each iv, the effect of one iv individually on the dv, to test for main effects, compare marginal means of dv for each. Interaction effect: the unique effect of a combination of ivs: the effect of one iv depends on the levels of the others iv(s) The effect of the music differs depending on whether you are doing math or reading. Example: music x task interaction: music reduces learning when studying reading, but enhances it when studying math: to test for an interaction effect, graph the cell of means. **see notes on how to graph no music line slopes down, while music line slopes up (they do intersect, not parallel), so you have an interaction. **age makes a difference but not a causal difference.
