## Type 3 p-value

This is a p-value for the composite null hypothesis that all levels of a categorical predictor have the same effect on the outcome as the reference category does. Results in the p-value column of regression output are instead for individual, specific null hypotheses that the level in that row has the same effect as the reference category. When the Type 3 p-value is small even though all the individual p-values are large, re-running the model with a different reference category may be more informative. The Type 3 p-value can also be >0.05 even when some of the individual p-values are <0.05; see Limitations of Omnibus Tests for further discussion.