# Goodness-of-fit for Fit Poisson Model

Find definitions and interpretation guidance for every statistic in the Goodness-of-fit tests table.

## Deviance Goodness-of-Fit Test

The deviance goodness-of-fit test assesses the discrepancy between the current model and the full model.

### Interpretation

Use the goodness-of-fit tests to determine whether the predicted numbers of events deviate from the observed numbers of events in a way that the Poisson distribution does not predict. If the p-value for the goodness-of-fit test is lower than your chosen significance level, you can reject the null hypothesis that the Poisson distribution provides a good fit. This list provides common reasons for deviations:
• Omitted higher-order term for variables in the model
• Omitted predictor that is not in the model
• Overdispersion

If the deviation is statistically significant, you can try a different link function or change the terms in the model.

## Pearson Goodness-of-Fit Test

The Pearson goodness-of-fit test assesses the discrepancy between the current model and the full model.

### Interpretation

Use the goodness-of-fit tests to determine whether the predicted numbers of events deviate from the observed numbers of events in a way that the Poisson distribution does not predict. If the p-value for the goodness-of-fit test is lower than your chosen significance level, you can reject the null hypothesis that the Poisson distribution provides a good fit. This list provides common reasons for deviations: