Contents
What is a second order interaction?
in analysis of variance or regression analysis, an effect in which three independent variables combine to have a nonadditive influence on a dependent variable.
What does adding interaction terms do?
Adding interaction terms to a regression model can greatly expand understanding of the relationships among the variables in the model and allows more hypotheses to be tested. Adding an interaction term to a model drastically changes the interpretation of all the coefficients.
Should you include interaction terms?
When the effect of one independent variable depends on the level of another independent variable, we have an interaction; and an interaction term should be included in the regression equation.
What does it mean to add interaction terms in regression?
You wrote: “But in regression, adding interaction terms makes the coefficients of the lower order terms conditional effects, not main effects. That means that the effect of one predictor is conditional on the value of the other.”. However, “the effect of one predictor is conditional on the value of the other” is precisely what “interaction” means.
When to add interaction terms in an ANOVA?
In an ANOVA, adding interaction terms still leaves the main effects as main effects. That is, as long as the data are balanced, the main effects and the interactions are independent. The main effect is still telling you if there is an overall effect of that variable after accounting for other variables in the model.
When to leave in significant two way interactions?
And as always, leave in any lower order terms, significant or not, for any higher order terms in the model. That means you have to leave in all insignificant two-way interactions for any significant 3-ways.
Which is an example of a 2 way interaction?
This means variables combine or interact to affect the response. The simplest type of interaction is the interaction between two two-level categorical variables. Let’s say we have gender (male and female), treatment (yes or no), and a continuous response measure. If the response to treatment depends on gender, then we have an interaction.