Often when we perform simple linear regression, we’re interested in creating a scatterplot to visualize the various combinations of x and y values.

Fortunately, R makes it easy to create scatterplots using the **plot() **function. For example:

#create some fake data data <- data.frame(x = c(1, 1, 2, 3, 4, 4, 5, 6, 7, 7, 8, 9, 10, 11, 11), y = c(13, 14, 17, 12, 23, 24, 25, 25, 24, 28, 32, 33, 35, 40, 41)) #create scatterplot of data plot(data$x, data$y)

It’s also easy to add a regression line to the scatterplot using the **abline() **function. For example:

#fit a simple linear regression model model <- lm(y ~ x, data = data) #add the fitted regression line to the scatterplot abline(model)

We can also add confidence interval lines to the plot by using the **predict() **function. For example:

#define range of x values newx = seq(min(data$x),max(data$x),by = 1) #find 95% confidence interval for the range of x values conf_interval <- predict(model, newdata=data.frame(x=newx), interval="confidence", level = 0.95) #create scatterplot of values with regression line plot(data$x, data$y) abline(model) #add dashed lines (lty=2) for the 95% confidence interval lines(newx, conf_interval[,2], col="blue", lty=2) lines(newx, conf_interval[,3], col="blue", lty=2)

Or we could instead add prediction interval lines to the plot by specifying the interval type within the **predict()** function. For example:

#define range of x values newx = seq(min(data$x),max(data$x),by = 1) #find 95% prediction interval for the range of x values pred_interval <- predict(model, newdata=data.frame(x=newx), interval="prediction", level = 0.95) #create scatterplot of values with regression line plot(data$x, data$y) abline(model) #add dashed lines (lty=2) for the 95% confidence interval lines(newx, pred_interval[,2], col="red", lty=2) lines(newx, pred_interval[,3], col="red", lty=2)

Lastly, we can make the plot more aesthetically pleasing by adding a title, changing the axes names, and changing the shape of the individual points in the plot.

plot(data$x, data$y, main = "Scatterplot of x vs. y", #add title pch=16, #specify points to be filled in xlab='x', #change x-axis name ylab='y') #change y-axis name abline(model, col='steelblue') #specify color of regression line