The “qqline” Function in R

• Package: Base R (stats package)

• Purpose: To add a line to a quantile-quantile (Q-Q) plot, typically used to compare the distribution of a dataset against a theoretical distribution (e.g. normal distribution).

• General Class: Statistical Visualization

• Required Argument(s):

• None (Arguments are typically supplied indirectly through the qqplot function).

• Notable Optional Arguments:

• probs: A numeric vector specifying the probabilities for the quantiles at which the line is drawn.

• col: changes the color of the line.

• Example:

• # Example usage
  # Generate a random sample from a normal distribution
  data <- rnorm(100)
  
  # Create a Q-Q plot using qqnorm
  qqnorm(data)
  
  # Add a line to the Q-Q plot using qqline
  qqline(data, col = "red")

• In this corrected example, qqnorm is used to create the Q-Q plot, and then qqline is used to add a red line to the plot, representing the expected quantiles for a normal distribution.