Table 6. Factors predicting HAQ-DI of 4 year follow-up determined by multiple regression analysis.

	Estimate	Standard error	P value
Intercept	−2.75	1.62	0.099
Log10 (serum P-selectin levels of baseline) ng/ml	2.22	0.96	0.028
%VC of baseline	−0.0060	0.0030	0.057
HAQ-DI of baseline	0.29	0.17	0.100

The multiple regression equations predicting HAQ-DI of 4 year follow-up are as follows; HAQ-DI of 4 year follow-up = −2.75+2.22×log₁₀(serum P-selectin levels (ng/ml) of baseline)+−0.0060×%VC of baseline +0.29×HAQ-DI of baseline. R² (determination coefficient) = 0.41, root mean square error = 0.345, p = 0.001.