Testing for Non-Stationarity in R

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In the second part of the series, we will be testing for non-stationarity using the Augmented Dickey-Fuller, the Phillips Perron Test, and the KPSS test.

Codes and Dataset are in here:

Created by Justin S. Eloriaga
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You had an oversight on the differenced KPSS test. The result of differenced inflation stationarity test using KPSS shows that inflation is stationary at first difference since the p-value is 0.1 which is 10%. Your videos are quite informative and very useful. Thanks for all you have been doing.

bolajiadedasola
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hi, great videos! One question, kpss(dinf) gives a p-value of 0.1, why do you say it's non-stationary?

estaykylyshbek
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Thanks for the nice explanation, i get confused sometimes when reporting unit root tests we take absolute value or consider the sign of value for example test that compares calculated t statistics with tabulated value example t calt= -2.56 and t tabulated= -4.63 In this do we reject null or except .

Thanks

bolisolwak
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Why does the p value shows 'NA' when I run adf test in R.

meenalchand
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Is it not a requirement to transform the data using a log before using KPSS test?

yonasabebe
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what if the results of the three test are contradictory??? both adf and kpss shows non stationarity at level however, the pp test shows stationarity. i tried differencing my data and then the adf and pp shows stationarity but my kpss shows non stationarity. it's very confusing

samfisher
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Thank you. Your videos are very helpful...

sajidnoor
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Mmm one question, does the number of lags to be chosen in the ADF test depend on the data frequency? For example if I have monthly data could I use 12 lags or something like that?

fvc
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Hi! Thanks for these videos, which are very helpful. One question: on the last test KPSS for dinf, we see a high p-value supporting the null hypothesis that the series is stationary: it is then agreeing with the rest of the tests to my understanding so why do you say the test indicates that dinf is non-stationary?

dumoncelclemence