面板数据协整检验(Stata)

当时间序列数据存在非平稳性时,直接将经济变量进行回归可能产生伪回归问题。针对非平稳数据计量建模,首先要判定这些变量是否存在同阶单整,如果满足同阶单整,才有必要对这些变量进行协整检验。当所涉及的变量存在协整时,由这些变量构建的回归模型才有意义,这也是区别于真实回归和虚假回归的标志。协整检验的前提是原始变量是非平稳的,或者变量具有单位根过程。因此在实际操作时,先对原始变量进行单位根检验,当所有变量都是非平稳,且同阶差分平稳时(或者同阶单整),才有必要采取协整检验。在Stata软件中,提供了Kao、pedroni和 westerlund三种检验方式,不同方式有其不同的适用条件,具体如下:

kao检验只能用于同质面板,命令选择项包括

  • lags(#)ADF检验滞后阶数#,见下文
  • kernel()协方差矩阵核估计方法,见下文
  • demean个体去均值

Pedroni检验适用于异质面板,命令选择项包括

  • ar(panelspecific|same) ADF检验中AR系数异质(默认)否
  • lags(#)ADF检验滞后阶数#
  • kernel()协方差矩阵核估计方法
  • demean个体去均值
  • trend 趋势效应
  • noconstant 无个体效应

westerlund检验适用于异质面板,命令选择项包括

  • trend 趋势效应
  • demean个体去均值
  • somepanles 一定比例的面板数据存在协整(默认)
  • allpanels 全部变量存在协整

其中ADF的检验形式包括:

  • # 表示滞后阶数,缺失默认为1
  • aic # 以aic准则确定最大滞后阶数 #
  • bic # 以bic准则确定最大滞后阶数 #
  • hqic # 以hqic准则确定最大滞后阶数 #

协方差核估计选择项包括:barlett newest 、barlett # 、parzen newest、parzen #、quadraticspectral newst、quadraticspectral #。上述三种检验的原假设为H0:变量间不存在协整关系;Kao、pedroni检验备择假设H1:全部变量之间存在协整关系。westerlund检验的备择假设存在两种形式,包括H1-a:全部变量存在协整关系;H1-b:存在一定比例的变量具有协整关系。


代码(Stata)操作如下:

* help xtcointtest
**# 1 数据准备
webuse xtcoint //调用网页数据
summarize rddomestic- productivity //描述统计

**# 2 单位根检验

xtunitroot ht productivity
/*
 xtunitroot ht productivity

Harris-Tzavalis unit-root test for productivity
-----------------------------------------------
H0: Panels contain unit roots               Number of panels  =    100
Ha: Panels are stationary                   Number of periods =    150

AR parameter: Common                        Asymptotics: N -> Infinity
Panel means:  Included                                   T Fixed
Time trend:   Not included
------------------------------------------------------------------------------
                    Statistic         z         p-value
------------------------------------------------------------------------------
 rho                  0.9822        0.9741       0.8350
------------------------------------------------------------------------------

*/
xtunitroot ht rddomestic
/*
Harris-Tzavalis unit-root test for rddomestic
---------------------------------------------
H0: Panels contain unit roots               Number of panels  =    100
Ha: Panels are stationary                   Number of periods =    150

AR parameter: Common                        Asymptotics: N -> Infinity
Panel means:  Included                                   T Fixed
Time trend:   Not included
------------------------------------------------------------------------------
                    Statistic         z         p-value
------------------------------------------------------------------------------
 rho                  0.9999        9.3783       1.0000
------------------------------------------------------------------------------

*/
xtunitroot ht rdforeign
/*
Harris-Tzavalis unit-root test for rdforeign
--------------------------------------------
H0: Panels contain unit roots               Number of panels  =    100
Ha: Panels are stationary                   Number of periods =    150

AR parameter: Common                        Asymptotics: N -> Infinity
Panel means:  Included                                   T Fixed
Time trend:   Not included
------------------------------------------------------------------------------
                    Statistic         z         p-value
------------------------------------------------------------------------------
 rho                  0.9990        8.9594       1.0000
------------------------------------------------------------------------------

*/

*以上结果表明productivity、rddomestic和rdforeign非平稳,接下来考虑一阶差分,再进行单位根检验

xtunitroot ht d.productivity,demean
/*

Harris-Tzavalis unit-root test for D.productivity
-------------------------------------------------
H0: Panels contain unit roots               Number of panels  =    100
Ha: Panels are stationary                   Number of periods =    149

AR parameter: Common                        Asymptotics: N -> Infinity
Panel means:  Included                                   T Fixed
Time trend:   Not included                  Cross-sectional means removed
------------------------------------------------------------------------------
                    Statistic         z         p-value
------------------------------------------------------------------------------
 rho                 -0.3755      -6.4e+02       0.0000
------------------------------------------------------------------------------
*/
xtunitroot ht d.rddomestic,demean 
/*
xtunitroot ht d.rddomestic,demean 

Harris-Tzavalis unit-root test for D.rddomestic
-----------------------------------------------
H0: Panels contain unit roots               Number of panels  =    100
Ha: Panels are stationary                   Number of periods =    149

AR parameter: Common                        Asymptotics: N -> Infinity
Panel means:  Included                                   T Fixed
Time trend:   Not included                  Cross-sectional means removed
------------------------------------------------------------------------------
                    Statistic         z         p-value
------------------------------------------------------------------------------
 rho                 -0.0039      -4.6e+02       0.0000
------------------------------------------------------------------------------

*/

xtunitroot ht d.rdforeign,demean 
/*
Harris-Tzavalis unit-root test for D.rdforeign
----------------------------------------------
H0: Panels contain unit roots               Number of panels  =    100
Ha: Panels are stationary                   Number of periods =    149

AR parameter: Common                        Asymptotics: N -> Infinity
Panel means:  Included                                   T Fixed
Time trend:   Not included                  Cross-sectional means removed
------------------------------------------------------------------------------
                    Statistic         z         p-value
------------------------------------------------------------------------------
 rho                 -0.0029      -4.6e+02       0.0000
------------------------------------------------------------------------------

*/

* 以上结果表明,所有变量满足一阶单整I(1),下面考虑协整

**# 3 协整检验
xtcointtest kao productivity rddomestic rdforeign //Kao检验
/*
Kao test for cointegration
--------------------------
H0: No cointegration                        Number of panels       =    100
Ha: All panels are cointegrated             Number of periods      =    148

Cointegrating vector: Same
Panel means:          Included              Kernel:           Bartlett
Time trend:           Not included          Lags:             3.60 (Newey–West)
AR parameter:         Same                  Augmented lags:   1 
------------------------------------------------------------------------------
                                            Statistic         p-value
------------------------------------------------------------------------------
 Modified Dickey–Fuller t                   -23.6733          0.0000
 Dickey–Fuller t                            -15.1293          0.0000
 Augmented Dickey–Fuller t                   -3.6909          0.0001
 Unadjusted modified Dickey–Fuller t        -46.7561          0.0000
 Unadjusted Dickey–Fuller t                 -20.2521          0.0000
------------------------------------------------------------------------------
*共有5个统计量,最后两个没有校正,主要看ADF检验
*/

xtcointtest pedroni productivity rddomestic rdforeign //pedroni检验
/*
Pedroni test for cointegration
------------------------------
H0: No cointegration                        Number of panels       =    100
Ha: All panels are cointegrated             Number of periods      =    149

Cointegrating vector: Panel specific
Panel means:          Included              Kernel:           Bartlett
Time trend:           Not included          Lags:             4.00 (Newey–West)
AR parameter:         Panel specific        Augmented lags:   1 
------------------------------------------------------------------------------
                                            Statistic         p-value
------------------------------------------------------------------------------
 Modified Phillips–Perron t                 -26.1145          0.0000
 Phillips–Perron t                          -21.2436          0.0000
 Augmented Dickey–Fuller t                  -25.3701          0.0000
------------------------------------------------------------------------------
三个统计量都具有参考价值
*/

xtcointtest westerlund productivity rddomestic rdforeign // westerlund检验,默认部分比例存在协整
/*
Westerlund test for cointegration
---------------------------------
H0: No cointegration                        Number of panels       =    100
Ha: Some panels are cointegrated            Number of periods      =    150

Cointegrating vector: Panel specific
Panel means:          Included
Time trend:           Not included
AR parameter:         Panel specific
------------------------------------------------------------------------------
                                            Statistic         p-value
------------------------------------------------------------------------------
 Variance ratio                              -8.0237          0.0000
------------------------------------------------------------------------------
*/

* 下面考虑将H1:全部变量存在协整 作为备择假设

xtcointtest westerlund productivity rddomestic rdforeign, allpanels
/*
Westerlund test for cointegration
---------------------------------
H0: No cointegration                        Number of panels       =    100
Ha: All panels are cointegrated             Number of periods      =    150

Cointegrating vector: Panel specific
Panel means:          Included
Time trend:           Not included
AR parameter:         Same
------------------------------------------------------------------------------
                                            Statistic         p-value
------------------------------------------------------------------------------
 Variance ratio                              -5.9709          0.0000
------------------------------------------------------------------------------
*/

** 以上结果表明,变量productivity rddomestic rdforeign存在协整,可以考虑非平稳建模,如面板向量误差修正模型等。

-END-
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