Ihtesham,
what´s the null hyphothesis that you are testing?
Ho: lCPI exhibits a unit root.
With these dfgls test statistics you can´t reject H0 at 10%. Test
Statistic < Critical Value for lags 1-15.
ICPI isn´t stationary.
HTH,
Joao Lima
2009/8/27 Ihtesham Afzal <[email protected]>:
> Thank you again.
>
> If I do decide to go with the -dfgls- command, could you please help me interpret the results? i.e. is the time-series stationary?
> . dfgls lCPI
>
> DF-GLS for lCPI Number of obs = 284
> Maxlag = 15 chosen by Schwert criterion
>
> DF-GLS tau 1% Critical 5% Critical 10% Critical
> [lags] Test Statistic Value Value Value
> ------------------------------------------------------------------------------
> 15 -0.614 -3.480 -2.815 -2.535
> 14 -0.659 -3.480 -2.823 -2.542
> 13 -0.787 -3.480 -2.830 -2.549
> 12 -1.235 -3.480 -2.838 -2.555
> 11 -0.351 -3.480 -2.845 -2.562
> 10 -0.285 -3.480 -2.851 -2.568
> 9 -0.223 -3.480 -2.858 -2.574
> 8 -0.327 -3.480 -2.865 -2.580
> 7 -0.381 -3.480 -2.871 -2.586
> 6 -0.457 -3.480 -2.877 -2.591
> 5 -0.254 -3.480 -2.883 -2.596
> 4 -0.164 -3.480 -2.888 -2.601
> 3 -0.084 -3.480 -2.894 -2.606
> 2 -0.233 -3.480 -2.899 -2.611
> 1 -0.206 -3.480 -2.903 -2.615
>
> Opt Lag (Ng-Perron seq t) = 13 with RMSE .0030169
> Min SC = -11.32856 at lag 13 with RMSE .0030169
> Min MAIC = -11.51094 at lag 14 with RMSE .003008
>
>
> Kind Regards
> Ihtesham
>
> ----------------------------------------
>> Date: Thu, 27 Aug 2009 16:31:36 +0100
>> Subject: Re: st: Appropriate lags for Augmented Dickey-Fuller Test
>> From: [email protected]
>> To: [email protected]
>>
>> -pperron- does not use lags to correct for serial correlation in the
>> Dickey-Fuller regressions and instead uses a Newey-West type robust
>> variance-covariance matrix to calulate the standard errors. However,
>> please see [TS] pperron documentation for cases when the
>> Phillips-Perron test is not applicable.
>>
>> If you are going to use -dfuller-, you might look at -varsoc- for
>> lag-length selection.
>>
>> You also do not specify a trend or drift terms in your -dfuller-. You
>> need to be sure that this is indeed the case, a very good preliminary
>> strategy is to visualise the data to see if there is a deterministic
>> trend in it.
>>
>> T
>>
>> 2009/8/27 Ihtesham Afzal :
>>>
>>> Thanks again for your reply.
>>> I think I will use the dfuller, lags(#) command as I think that is sufficient for the test I am lookinf to do
>>> Just one question though. I was made aware that I dont need to include a lags(#) term for the Phillips-Perron test does not need the lagged values.
>>> Is this correct?
>>> Thank you
>>> Regards
>>> Ihtesham
>>> ----------------------------------------
>>>> Date: Thu, 27 Aug 2009 13:58:57 +0100
>>>> Subject: Re: st: Appropriate lags for Augmented Dickey-Fuller Test
>>>> From: [email protected]
>>>> To: [email protected]
>>>>
>>>> Not really. -dfuller- provides what are called parametric augmented
>>>> Dickey-Fuller (ADF) tests, which require explicit specification of the
>>>> (linear) trend component. -dfgls- belongs to a class of efficient ADF
>>>> unit root tests, which involve running the ADF tests on
>>>> quasi-differenced series (wherby a trend is extracted by GLS
>>>> detrending) - leading, typically, to greater power properties.
>>>>
>>>> In either case, -dfuller- does not include a trend by default and
>>>> -dfgls- does. So as you are using them, they are not comparable. For
>>>> quick diagnostics on unit roots, I prefer -dfgls-.
>>>>
>>>> I can point you to the excellent exposition in Phillips and Xiao
>>>> (1998) & [TS] dfgls.
>>>>
>>>> --- References ---
>>>> @article{phillips1998primer,
>>>> title={{A Primer on Unit Root Testing}},
>>>> author={Phillips, P.C.B. and Xiao, Z.},
>>>> journal={Journal of Economic Surveys},
>>>> volume={12},
>>>> number={5},
>>>> pages={423--470},
>>>> year={1998},
>>>> publisher={Blackwell Publishers Ltd}
>>>> }
>>>>
>>>>
>>>>
>>>> 2009/8/27 Ihtesham Afzal :
>>>>> Hello, first of all, thanks for the reply.
>>>>> Here is the output. From this can I infer that the lags i should use is 14 (if I use the MAIC)and thus conduct the ADF test with 14 lags as I have done below?
>>>>> Is this the correct procedure.
>>>>> Kinds Regards.
>>>>> Ihtesham
>>>>>
>>>>>
>>>>> . dfgls lCPI
>>>>>
>>>>> DF-GLS for lCPI Number of obs = 284
>>>>> Maxlag = 15 chosen by Schwert criterion
>>>>>
>>>>> DF-GLS tau 1% Critical 5% Critical 10% Critical
>>>>> [lags] Test Statistic Value Value Value
>>>>> ------------------------------------------------------------------------------
>>>>> 15 -0.614 -3.480 -2.815 -2.535
>>>>> 14 -0.659 -3.480 -2.823 -2.542
>>>>> 13 -0.787 -3.480 -2.830 -2.549
>>>>> 12 -1.235 -3.480 -2.838 -2.555
>>>>> 11 -0.351 -3.480 -2.845 -2.562
>>>>> 10 -0.285 -3.480 -2.851 -2.568
>>>>> 9 -0.223 -3.480 -2.858 -2.574
>>>>> 8 -0.327 -3.480 -2.865 -2.580
>>>>> 7 -0.381 -3.480 -2.871 -2.586
>>>>> 6 -0.457 -3.480 -2.877 -2.591
>>>>> 5 -0.254 -3.480 -2.883 -2.596
>>>>> 4 -0.164 -3.480 -2.888 -2.601
>>>>> 3 -0.084 -3.480 -2.894 -2.606
>>>>> 2 -0.233 -3.480 -2.899 -2.611
>>>>> 1 -0.206 -3.480 -2.903 -2.615
>>>>>
>>>>> Opt Lag (Ng-Perron seq t) = 13 with RMSE .0030169
>>>>> Min SC = -11.32856 at lag 13 with RMSE .0030169
>>>>> Min MAIC = -11.51094 at lag 14 with RMSE .003008
>>>>>
>>>>>
>>>>> . dfuller lCPI, lags(14)
>>>>> Augmented Dickey-Fuller test for unit root Number of obs = 285
>>>>> ---------- Interpolated Dickey-Fuller ---------
>>>>> Test 1% Critical 5% Critical 10% Critical
>>>>> Statistic Value Value Value
>>>>> ------------------------------------------------------------------------------
>>>>> Z(t) -1.980 -3.457 -2.879 -2.570
>>>>> ------------------------------------------------------------------------------
>>>>> MacKinnon approximate p-value for Z(t) = 0.2955
>>>>>
>>>>>
>>>>> ----------------------------------------
>>>>>> Date: Thu, 27 Aug 2009 12:59:34 +0100
>>>>>> Subject: Re: st: Appropriate lags for Augmented Dickey-Fuller Test
>>>>>> From: [email protected]
>>>>>> To: [email protected]
>>>>>>
>>>>>> <>
>>>>>> -dfgls- reports three different criteria for lag selection:
>>>>>>
>>>>>> 1) Ng-Perron
>>>>>> 2) Schwarz
>>>>>> 3) Modified AIC
>>>>>>
>>>>>> and reports tests upto a max. lag determined by the Schwert criteria.
>>>>>>
>>>>>> T
>>>>>>
>>>>>> On Thu, Aug 27, 2009 at 12:39 PM, Ihtesham
>>>>>> Afzal wrote:
>>>>>>> Hello.
>>>>>>> Just a quick question.
>>>>>>> When undergoing the Augmented Dickey Fuller Test, how do I decide on how many lags to include for each series?
>>>>>>> Do I estimate the AR(p) model with different p-lag values and then find the one with the lowest AIC/BIC value?
>>>>>>>
>>>>>>> Kind Regards.
>>>>>>>
>>>>>>> Ihtesham
>>>>>>> _________________________________________________________________
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>>>>>>
>>>>>>
>>>>>>
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>>>>
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>>
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--
----------------------------------------
Joao Ricardo Lima, D.Sc.
Professor
UFPB-CCA-DCFS
Fone: +5538387264913
Skype: joao_ricardo_lima
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