# Interaction Model

Let’s look at the interaction model in multiple regression.

Let’s now quantify the relationship of our outcome variable

We’ll write out the equation of the two regression lines using the values from a regression table. Before we do this, however, let’s go over a brief refresher of regression when we have a categorical explanatory variable

Recall how we fit a regression model for countries’ life expectancies as a function of which continent the country was in. In other words, we had a numerical outcome variable `lifeExp`

and a categorical explanatory variable `continent`

, which had five levels—`Africa`

, the `Americas`

, `Asia`

, `Europe`

, and `Oceania`

. Let’s redisplay the regression table:

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