Click here to download the source R Markdown file: `multiple_regression.Rmd`

. For this R Markdown file to “knit” you’ll need to ensure you’ve installed the “development” version of the `moderndive`

package by running:

```
library(devtools)
install_github("moderndive/moderndive", ref = "geom_parallel_slopes")
```

Let’s use the same data as in Jenny and Albert’s example project proposal.

school_name | average_sat_math | percent_economically_disadvantaged | school_size |
---|---|---|---|

Newton South High | 620 | 8.8 | large |

Quincy High | 502 | 34.7 | large |

Hopedale Jr Sr High | 535 | 9.0 | medium |

Madison Park High | 358 | 68.1 | large |

Center For Technical Education Innovation | 555 | 36.5 | large |

An interaction model is flexible: it allows for different slopes and different intercepts.

To plot an interaction model, we use `geom_smooth()`

like we did in Chapter 6. Note that while the three lines at first glance seem parallel, they aren’t quite.

```
ggplot(ma_schools, aes(x = percent_economically_disadvantaged, y = average_sat_math, color = school_size))+
geom_point() +
geom_smooth(method = "lm", se = FALSE ) +
labs(y = "Math SAT Score", x = "Percentage of Economically Disadvantaged Students")
```