PSY 350 Lecture Notes - Lecture 40: Toothpaste
Document Summary
Differentiate an interaction from the sum of two main effects. An interaction occurs when the effect of one independent/predictor variable on the dependent variable changes depending on the level of another independent/predictor variable. An interaction does not mean that one iv/predictor affects another predictor variable, which in turn affects the outcome. In an experiment one iv cannot affect the other--by design! If each iv has a separate effect on the outcome, the combination of the two effects is not necessarily an interaction. We call the effect of each iv, by itself, a main effect. Often, two (or more) variables have their own main effects on an outcome. If the presence of one variable makes no difference to the effect of the other, there is no interaction. However, if the two main effects may be additive, so that having both ivs is better than having just one. For example: i like hats and i like corgis.
