```
library(tidyverse)
library(tidymodels)
library(openintro)
library(knitr)
```

# AE 3: Duke Forest houses

Checking model conditions

## Packages

## Predict sale price from area

```
<- linear_reg() %>%
df_fit set_engine("lm") %>%
fit(price ~ area, data = duke_forest)
tidy(df_fit) %>%
kable(digits = 2)
```

term | estimate | std.error | statistic | p.value |
---|---|---|---|---|

(Intercept) | 116652.33 | 53302.46 | 2.19 | 0.03 |

area | 159.48 | 18.17 | 8.78 | 0.00 |

## Model conditions

### Exercise 1

The following code produces the residuals vs. fitted values plot for this model. Comment out the layer that defines the y-axis limits and re-create the plot. How does the plot change? Why might we want to define the limits explicitly?

```
<- augment(df_fit$fit)
df_aug
ggplot(df_aug, aes(x = .fitted, y = .resid)) +
geom_point() +
geom_hline(yintercept = 0, linetype = "dashed") +
ylim(-1000000, 1000000) +
labs(
x = "Fitted value", y = "Residual",
title = "Residuals vs. fitted values"
)
```

### Exercise 2

Improve how the values on the axes of the plot are displayed by modifying the code below.

Hint: use `scale_continuous()`

```
ggplot(df_aug, aes(x = .fitted, y = .resid)) +
geom_point() +
geom_hline(yintercept = 0, linetype = "dashed") +
ylim(-1000000, 1000000) +
labs(
x = "Fitted value", y = "Residual",
title = "Residuals vs. fitted values"
)
```