Table 3. Comparisons of fractional polynomial models.

The model selection was performed using closed test procedure. By comparing to the model without variable (omitted model), the two-term model (m = 2) was significantly better with a difference of deviance of 34.8. However, the two-term model was not significantly better than the linear model (difference of deviance: 2.5; p = 0.111), and thus the linear model was adopted for simplicity.

Mean balance	Degree of freedom	Deviance	Difference of deviance	p	Powers
Omitted	0	257.927	34.789	0.000
Linear	1	225.680	2.542	0.111	1
m = 1	1	223.775	0.637	0.425	3
m = 2	2	223.138	0.000	–	3 3