Poisson Regression

Deviance Residuals versus Fits

This graph plots the residuals versus the fitted values. 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
Curvilinear	A missing higher-order term
A point far away from zero	An outlier
A point far away from the other points in the x-direction	An influential point

Example Output

Interpretation

For the resin defect data, there is a clear curve in the data. This pattern reveals a problem with the model. In this case, the analysts find that interactions that are in the data are not in the model.