Binary Logistic Regression

Residual Plots - Residuals versus fits

This graph plots the residuals versus the fitted values. When the data are in event/trial format and have repeated observations at the predictor values, the interpretation is similar to least squares regression. The residuals should be scattered randomly about zero. Use this plot to look for the following:

This pattern...	Indicates...
Fanning or uneven spreading of residuals across fitted values	Nonconstant variance or an inappropriate link function
Curvilinear	A missing higher-order term or an inappropriate link function
A point far away from zero	An outlier
A point far away from the other points in the x-direction	An influential point

If the data do not have repeated observations at the predictor values, the plot shows two groups of points that approximate lines. This pattern is not informative.

Example Output

Interpretation

For the cereal data, the residuals have two groups of points that approximate lines. Because few customers have the same income, only a few predictor values repeat. The pattern that appears is not informative.

The data in the sample folder is not in event/trial format. See Change from binary response format to event/trial format to learn how to produce this plot.