Table 2. Multiple linear regression on bone metabolism biomarkers.

Dependent variable	Indicators of plasmapheresis donation behaviors	Unstandardized coefficients		Standardized coefficients beta	t	Sig.	Collinearity statistics
		B	Std. error				Tolerence	VIF
25OHD	Total numbers	0.021	0.005	0.239	4.458	<0.001	0.38	2.63
	Recent frequency	−0.29	0.046	−0.386	−6.367	<0.001	0.297	3.365
P1NP	Total numbers	0.036	0.022	0.093	1.663	0.037	0.534	1.874
β-CTX	Recent frequency	−0.002	0.001	−0.122	−2.336	0.02	0.635	1.576
PTH	Recent frequency	0.368	0.14	0.185	2.621	0.009	0.544	1.839