1996年

2008年

2019年

Estimate

VIF

Estimate

VIF

Estimate

VIF

(Intercept)

0.9137

1.2453

0.8272

lnpgdp

−0.2335

4.8754

−0.5627

6.8645

0.2069

2.4142

global

0.0949

1.6226

0.1016

8.6523

−0.4667

5.6602

upgrade

0.2971

3.4426

0.0797

2.5208

0.2824

3.3159

education

−0.7857

2.2364

−0.7323

2.1570

−0.8438

2.0508

highway

−0.2088

2.7421

−0.1405

1.5895

−0.1037

1.4830

Adjust-R²

0.4129

0.6959

0.561