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Unformatted text preview: Interaction effects between continuous variables—Page 1 Interaction effects between continuous variables This is a very brief overview of this somewhat difficult topic. The course readings provide much more detail, and you should go over these carefully if you feel these kinds of interaction terms will be useful in your work. We’ll probably just cover this quickly in class, or else I’ll let you cover it on your own. Interactions between two continuous variables. We have focused on interactions between categorical and continuous variables. However, there can also be interactions between two continuous variables. For example, suppose that “Intentions” and “Actual Behavior” are both measured as continuous variables. Suppose further it is believed that the effect of intentions on behavior (i.e. the correspondence between what one wants to do and what one actually does) is greater at higher levels of income; that is, the higher one’s income is, the more consistently one behaves. This model would be written as Behavior Intentions Income Intentions Income Income Intentions Income Intentions Intentions Income 1 2 3 1 3 2 1 2 3 ( * ) ( * ) ( * )* A positive value for the effect of the interaction term would imply that the higher the income, the greater (more positive) the effect of intentions on behavior was. Similarly, the higher the intentions, the greater (more positive) the effect of income on behavior. E XAMPLES . The greater the resources available, the stronger the effect of intentions on behavior. Those who are most able to get what they want are most likely to get it. The more religious someone is, the stronger the effect of moral values on behavior. The more religious someone is, the more compelled they will be to act on their moral values. Interpreting Interactions between two continuous variables. As Jaccard, Turrisi and Wan (Interaction effects in multiple regression) and Aiken and West (Multiple regression: Testing and interpreting interactions) note, there are a number of difficulties in interpreting such interactions....
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- Spring '11
- main effect