Table 4. Model comparison for the evaluation of additivity of anemia and renal impairment.

Model	AIC	χ2-statistic of model	p>χ2 of model	χ2-statistic of comparison	p>χ2 of comparison
1) Anemia only	6777.29	LR χ2 (1): 75.81	<0.001	LR χ2 (1) model 1 vs. null model: 75.81	<0.001
2) Renal impairment only	6750.89	LR χ2 (1): 102.21	<0.001	LR χ2 (1) model 2 vs. null model: 102.21	<0.001
3) Additive effect of anemia and renal impairment	6707.43	LR χ2 (2): 147.67	<0.001	LR χ2 (1) model 3 vs. model 2: 45.46	<0.001
4) Multiplicative interaction: anemia x renal impairment	6709.37	LR χ2 (3): 147.73	<0.001	LR χ2 (1) model 4 vs. model 3: 0.06	0.810

The first two models are compared to the null model, while model 3 is compared to model 2 (higher χ²-statistic as model 1) and model 4 to model 3 (higher χ²-statistic as model 2).