What is the name of the graph used to assess if the error term follows a normal distribution?

The graph used to assess whether the error term follows a normal distribution is known as a Normal probability plot. This type of plot is specifically designed to evaluate if a set of data points approximates a normal distribution. In a Normal probability plot, the theoretical quantiles of a normal distribution are plotted against the actual quantiles of the data being examined. If the points follow a roughly straight line, it indicates that the data distribution is close to normal.

This is crucial for many statistical analyses, particularly in regression, where the assumption of normally distributed errors is foundational to deriving valid conclusions from the model. By visually assessing the pattern formed in the plot, researchers can quickly ascertain if the underlying assumptions of their analysis are met, guiding further steps in the modeling process.