Poisson Regression

Modifying the Model

For this model and this set of data, there does not appear to be sufficient explanatory power in the YEAR*PERIOD effect to include it in the model.

Click on YEAR*PERIOD in the fit window.

Choose Edit:Delete from the menu.

Figure 17.8: Modified Fit Model

Follow the previous steps to remove the other two interaction terms from the model. The resulting main effects model is shown in Figure 17.9.

Figure 17.9: Main Effects Model

The estimate of the dispersion parameter ${{\phi} = {\sigma}^2 = 1.6910}$ suggests that overdispersion exists in the model. Type III (Wald) Tests table shows that all of the main effects are significant.

Parameter Estimates

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