Table 2 Estimation and statistical significance of the parameters of the selected regression models

[3] SI = α + β ∗ STPI^S + γ ∗ LP^λ + ξ ∗ E

α

16.47

1.84

< 0.0001

149.5

160.3

β

− 4.73

1.26

0.0006

γ

− 3.99

0.57

< 0.0001

λ

1.72

0.64

0.0095

ξ

2.36

1.12

0.0411

[11] \( \mathrm{SI}=\alpha +\beta \ast {\mathrm{STPI}}^S+\gamma \ast {\mathrm{LP}}^{\uplambda}+\xi \ast {P}_5^{\uprho} \)

α

15.88

1.06

< 0.0001

126.4

139.0

β

− 3.41

0.99

0.0014

γ

− 2.90

0.51

< 0.0001

λ

2.65

1.03

0.0139

ξ

1.15

0.41

0.0078

ρ

14.80

5.04

0.0056