---
title: "Lab 11"
author: "Your Name Here"
date: ""
output: html_document
---
##### Remember to change the `author: ` field on this Rmd file to your own name.
### Learning objectives
> In today's Lab you will gain practice with the following concepts from today's class:
>- Interpreting linear regression coefficients of numeric covariates
- Interpreting linear regression coefficients of categorical variables
- Fitting linear regression models with interaction terms
- Interpreting linear regression coefficients of interaction terms
We'll begin by loading some packages and importing the data.
```{r}
library(tidyverse)
```
```{r, echo = FALSE}
# Load data from MASS into a tibble and do pre-processing
birthwt <- as_tibble(MASS::birthwt) %>%
rename(birthwt.below.2500 = low,
mother.age = age,
mother.weight = lwt,
mother.smokes = smoke,
previous.prem.labor = ptl,
hypertension = ht,
uterine.irr = ui,
physician.visits = ftv,
birthwt.grams = bwt) %>%
mutate(race = recode_factor(race, `1` = "white", `2` = "black", `3` = "other")) %>%
mutate_at(c("mother.smokes", "hypertension", "uterine.irr", "birthwt.below.2500"),
~ recode_factor(.x, `0` = "no", `1` = "yes"))
```
### Interaction terms in regression
**(a)** Run a linear regression to better understand how birthweight varies with the mother's age and smoking status (do not include interaction terms).
```{r}
# Edit me
```
**(b)** What is the coefficient of mother.age in your regression? How do you interpret this coefficient?
```{r}
# Edit me
```
**(c)** How many coefficients are estimated for the mother's smoking status variable? How do you interpret these coefficients?
```{r}
# Edit me
```
**(d)** What does the intercept mean in this model?
**(e)** Using ggplot, construct a scatterplot with birthweight on the y-axis and mother's age on the x-axis. Color the points by mother's smoking status, and add smoking status-specific linear regression lines using the `stat_smooth` layer.
```{r}
# Edit me
```
**(f)** Do the regression lines plotted in part (e) correspond to the model you fit in part (a)? How can you tell?
**(g)** Fit a linear regression model that now models potential interactions between mother's age and smoking status in their effect on birthweight.
```{r}
# Edit me
```
**(h)** Interpret your model. Is the interaction term statistically significant? What does it mean?
```{r}
# Edit me
```