Table 2.

Threshold effect test.

The number of thresholds	RSS	MSE	F value	P value	10% Critical value	5% Critical value	1% Critical value
Single threshold	18.7556	0.0462	110.16	0.0000	35.8120	42.7288	55.8570
Double-threshold	16.2103	0.0399	63.75	0.0000	24.6645	29.6731	44.1526
Triple-threshold	19.6939	0.0485	11.61	0.1200	12.2799	24.7410	36.2274