② 异方差检验(WHITE检验)
利用Eviews进行White检验
White Heteroskedasticity Test:
F-statistic 0.532181 Probability 0.717072
Obs*R-squared 2.798276 Probability 0.592130
Test Equation:
Dependent Variable: RESID^2
Method: Least Squares
Date: 04/29/05 Time: 20:55
Sample: 1992 2003
Included observations: 12
Variable Coefficient Std. Error t-Statistic Prob.
C 354.0290 2564.535 0.138048 0.8941
X1 -1.207412 1.230960 -0.980871 0.3593
X1^2 0.000122 0.000185 0.657382 0.5319
X6 4.402393 4.986409 0.882879 0.4066
X6^2 -0.001670 0.001740 -0.959932 0.3691
R-squared 0.233190 Mean dependent var 294.5603
Adjusted R-squared -0.204988 S.D. dependent var 389.4829
S.E. of regression 427.5429 Akaike info criterion 15.24832
Sum squared resid 1279550. Schwarz criterion 15.45037
Log likelihood -86.48994 F-statistic 0.532181
Durbin-Watson stat 2.626586 Prob(F-statistic) 0.717072
因为Obs*R-squared=2.798276< X20.05(k-1).所以接受H0,表明模型没有异方差。
③ 自相关检验 (DW检验)
由结果显示DW=1.409856(计算得ρ=0.295072),而通过查表的dL=0.812,dU=1.579,4-dU=2.421,4-dL=3.188,可见dL<DW<dL,所以X1、X5有无自相关无法确定,需要进行修正。
现采用广义差分法进行修正,在GENR中输入DY=Y-0.295072*Y(-1),DX=X-0.295072*X(-1),再用OLS法进行估计,结果为:
Dependent Variable: DY
Method: Least Squares
Date: 04/29/05 Time: 21:47
Sample(adjusted): 1993 2003
Included observations: 11 after adjusting endpoints
Variable Coefficient Std. Error t-Statistic Prob.
C -14.59432 18.17540 -0.802971 0.4452
DX1 0.048412 0.017968 2.694321 0.0273
DX5 0.201696 0.061089 3.301653 0.0108
R-squared 0.989306 Mean dependent var 395.4397
Adjusted R-squared 0.986632 S.D. dependent var 133.9224
S.E. of regression 15.48417 Akaike info criterion 8.544515
Sum squared resid 1918.077 Schwarz criterion 8.653032
Log likelihood -43.99483 F-statistic 370.0250
Durbin-Watson stat 1.647507 Prob(F-statistic) 0.000000
这时,DW=1.647507,查表得dL=0.658,dU=1.604,从而DW>dU,可见DW已经落在了无自相关区域,表明通过修正的模型已经不存在自相关。
通过以上的回归及检验,就可得到以下回归方程:
DY= -14.59432 +0.048412DX1 +0.201696DX5
(-0.802971) (2.694321) (3.301653)
R2=0.989306 F=370.0250 DW=1.647507