Estimated results

Sample period

1983-1987

1988-1992

1993-1997

1998-2002

2003-2007

2008-2012

Model 1

Model 2

Model 3

Model 4

Model 5

Model 6

The linear part of the model

π₂

3.756(0.944)***

3.774(1.105)***

4.527(1.463)***

9.313(1.135)***

18.485(3.308)***

23.128(4.080)***

The nonlinear part of the model

θ₂

25.225(7.404)***

15.119(7.272)**

11.682(23.677)

42.108(46.399)

4.536(2.359)*

9.375(6.552)

γ

39.400(22.385)*

6.843(2.968)**

7.464(4.378)*

15.396(6.739)**

4.088(2.707)

6.271(4.657)

c

26.892(0.222)***

25.530(0.624)***

25.364(0.459)***

27.156(0.421)***

26.477(0.802)***

26.884(0.771)***

Adj. R²

0.932

0.937

0.945

0.916

0.863

0.830

SD of residuals

8.511

10.119

12.452

20.391

27.474

32.726

AIC

4.564

4.893

5.681

6.278

6.806

7.643

NO. of observations

53

53

53

52

54

53