Interaction between two continuous variables

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Statistical programs, like SPSS, do not always have "point-and-click" commands for every possible statistical test. This page is a description of how to test the interaction between two continuous variables. Three approaches are described below:
(1) three steps to conduct the interaction using commands within SPSS, and
(2) Interaction! software by Daniel S. Soper that performs statistical analysis and graphics for interactions between dichotomous, categorical, and continuous variables.
(3) R commands for executing the analysis.

*For a description of what is an interaction and main effects, please see the accompanying page about What is an Interaction?.


Three Steps using SPSS

There are three steps involved to calculate the interaction between two continuous variables.

Center the two continuous variables

Create the interaction term

Conduct Regression

Interaction! software

R commands

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