arch.unitroot.cointegration.phillips_ouliaris¶

arch.unitroot.cointegration.
phillips_ouliaris
(y, x, trend='c', *, test_type='Zt', kernel='bartlett', bandwidth=None, force_int=False)[source]¶ Test for cointegration within a set of time series.
 Parameters
y (array_like) – The lefthandside variable in the cointegrating regression.
x (array_like) – The righthandside variables in the cointegrating regression.
trend ({"n","c","ct","ctt"}, default "c") –
Trend to include in the cointegrating regression. Trends are:
”n”: No deterministic terms
”c”: Constant
”ct”: Constant and linear trend
”ctt”: Constant, linear and quadratic trends
test_type ({"Za", "Zt", "Pu", "Pz"}, default "Zt") –
The test statistic to compute. Supported options are:
”Za”: The Zα test based on the the debiased AR(1) coefficient.
”Zt”: The Zt test based on the tstatistic from an AR(1).
”Pu”: The Pᵤ varianceratio test.
”Pz”: The Pz test of the trace of the product of an estimate of the longrun residual variance and the innerproduct of the data.
See the notes for details on the test.
kernel (str, default "bartlett") – The string name of any of any known kernelbased longrun covariance estimators. Common choices are “bartlett” for the Bartlett kernel (NeweyWest), “parzen” for the Parzen kernel and “quadraticspectral” for the Quadratic Spectral kernel.
bandwidth (int, default None) – The bandwidth to use. If not provided, the optimal bandwidth is estimated from the data. Setting the bandwidth to 0 and using “unadjusted” produces the classic OLS covariance estimator. Setting the bandwidth to 0 and using “robust” produces White’s covariance estimator.
force_int (bool, default False) – Whether the force the estimated optimal bandwidth to be an integer.
 Returns
Results of the PhillipsOuliaris test.
 Return type
See also
arch.unitroot.ADF()
Augmented DickeyFuller testing.
arch.unitroot.PhillipsPerron()
Phillips & Perron’s unit root test.
arch.unitroot.cointegration.engle_granger()
Engle & Granger’s cointegration test.
Notes
Warning
The critical value simulation is ongoing and so the critical values may change slightly as more simulations are completed. These are still based on far more simulations (minimum 2,000,000) than were possible in 1990 (5000) that are reported in 1.
Supports 4 distinct tests.
Define the crosssectional regression
\[y_t = x_t \beta + d_t \gamma + u_t\]where \(d_t\) are any included deterministic terms. Let \(\hat{u}_t = y_t  x_t \hat{\beta} + d_t \hat{\gamma}\).
The Zα and Zt statistics are defined as
\[\begin{split}\hat{Z}_\alpha & = T \times z \\ \hat{Z}_t & = \frac{\hat{\sigma}_u}{\hat{\omega}^2} \times \sqrt{T} z \\ z & = (\hat{\alpha}  1)  \hat{\omega}^2_1 / \hat{\sigma}^2_u\end{split}\]where \(\hat{\sigma}^2_u=T^{1}\sum_{t=2}^T \hat{u}_t^2\), \(\hat{\omega}^2_1\) is an estimate of the onesided strict autocovariance, and \(\hat{\omega}^2\) is an estimate of the longrun variance of the process.
The \(\hat{P}_u\) varianceratio statistic is defined as
\[\hat{P}_u = \frac{\hat{\omega}_{11\cdot2}}{\tilde{\sigma}^2_u}\]where \(\tilde{\sigma}^2_u=T^{1}\sum_{t=1}^T \hat{u}_t^2\) and
\[\hat{\omega}_{11\cdot 2} = \hat{\omega}_{11}  \hat{\omega}'_{21} \hat{\Omega}_{22}^{1} \hat{\omega}_{21}\]and
\[\begin{split}\hat{\Omega}=\left[\begin{array}{cc} \hat{\omega}_{11} & \hat{\omega}'_{21}\\ \hat{\omega}_{21} & \hat{\Omega}_{22} \end{array}\right]\end{split}\]is an estimate of the longrun covariance of \(\xi_t\), the residuals from an VAR(1) on \(z_t=[y_t,z_t]\) that includes and trends included in the test.
\[z_t = \Phi z_{t1} + \xi_\tau\]The final test statistic is defined
\[\hat{P}_z = T \times \mathrm{tr}(\hat{\Omega} M_{zz}^{1})\]where \(M_{zz} = \sum_{t=1}^T \tilde{z}'_t \tilde{z}_t\), \(\tilde{z}_t\) is the vector of data \(z_t=[y_t,x_t]\) detrended using any trend terms included in the test, \(\tilde{z}_t = z_t  d_t \hat{\kappa}\) and \(\hat{\Omega}\) is defined above.
The specification of the \(\hat{P}_z\) test statistic when trend is “n” differs from the expression in 1. We recenter \(z_t\) by subtracting the first observation, so that \(\tilde{z}_t = z_t  z_1\). This is needed to ensure that the initial value does not affect the distribution under the null. When the trend is anything other than “n”, this set is not needed and the test statistics is identical whether the first observation is subtracted or not.
References