regions

S1

S2

S3

F2

F3

Conclusions

China

0.25346

2.64927

11.52231

1.95946

7.67925

Variable coefficient model

The east

0.09884

0.76223

3.68458

1.49179

6.70836

Variable intercept model

The central

0.04195

0.26568

2.43541

1.24853

11.12123

Variable intercept model

The west

0.11373

0.84357

2.55789

1.42157

3.96557

Variable intercept model