Overview of this book

R Graph Essentials
Credits
www.PacktPub.com
Preface
Free Chapter
Base Graphics in R – One Step at a Time
Advanced Functions in Base Graphics
Creating Graphs with ggplot
Index

Including regression lines

In `ggplot`, you can include regression lines using `geom_abline()`. For the next example, we set up the same graph of patient height against weight that we have used several times before:

```P <- ggplot(T, aes(x = HEIGHT, y = WEIGHT_1)) + geom_point()
```

As a start, let's calculate the slope and intercept of the line of best fit (regression line) for height against weight before treatment. In Chapter 1, Base Graphics in R – One Step at a Time, in the section entitled Including a regression line, we saw how to include a linear regression line on a graph. Now, we use the `lm()` command again to fit a linear regression model by using the following syntax:

```lm(WEIGHT_1 ~ HEIGHT, data = T)
```

Here is the output that you will see on your screen:

```Call:
lm(formula = WEIGHT_1 ~ HEIGHT, data = T)
Coefficients:
(Intercept)       HEIGHT
-123.611        1.166
```

So, the intercept is approximately -123.61 and the slope is approximately 1.17. You can now include the regression line...