A histogram of the standardized residuals shows the distribution of the residuals for all observations. Use the histogram as an exploratory tool to learn about the following characteristics of the data:

·    Typical values, spread or variation, and shape

·    Unusual values in the data

The histogram of the residuals should be bell-shaped. Use this plot to look for the following:

Because the appearance of the histogram can change depending on the number of intervals used to group the data, use the normal probability plot and goodness-of-fit tests to assess whether the residuals are normal.

For the soybean data, there are two histograms, one for moisture and one for fat.

·    The histogram of the standardized residuals for moisture reveals possible outliers in the data, indicated by the bars on the far right side of the plot.

·    The histogram of the standardized residuals for fat reveals a bell-shaped, symmetric pattern, indicating the residuals are not skewed and there are no outliers.