A unit root is a property of a non-stationary time series which can lead to spurious regressions and wrong inference.

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Cointegration between a variable of significant seasonality and one with no significant seasonality

After running programs of deseasonalization, I had an output in which one variable held significant seasonality, for which I corrected, and another that did not have. My main objective was to ...
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1answer
45 views

Explosive processes, non-stationarity and unit roots, how to distinguish?

I understand that if we have a simple model such as: $Y_t$=$\rho$$Y_{t-1}$+$\epsilon_t$ where $\rho$ is less than one in absolute value then we have a stationary process. If $\rho$ equals one then ...
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2answers
34 views

Which is the best criterion for DF-GLS lag selection?

When you have an output such as this in Stata for dfgls: ...
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1answer
22 views

Is there an optmal lag choice in the KPSS test?

Is there an optimal lag choice in the KPSS test in Stata? For instance, in my example below, for some lags (less than 7) you reject the null for any level of significance. But afterwards, that does ...
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0answers
10 views

Augmented Dickey-Fuller test with time trend term

I have time series variable X, Y and Z. I need to analyse these variables by using a VAR model. Before running a regression I did augmented Dickey-Fuller test and found that one variable is stationary ...
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2answers
49 views

Stationarity after differencing

I have the following two processes: \begin{align} x_t &= x_{t-1} + u_t \tag{1} \\ x_t &= {\beta}_0 + {\beta}_1t + u_t \tag{2} \end{align} Differencing once leads to: \begin{align} \Delta ...
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1answer
53 views

Lag selection for Augmented Dickey Fuller test

Apologies in advance, I am a beginner so these questions might be quite simple. I am testing log real exchange rates for unit root stationarity for EU15 countries. I was wondering what is the best way ...
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3answers
109 views

Estimation of unit-root AR(1) model with OLS

Given a random walk $x_t$, $$x_t=x_{t-1}+\varepsilon_t,$$ consider estimating the slope coefficient $\beta$ in $$x_t=\beta x_{t-1}+\varepsilon_t$$ by OLS. This question and the following answer ...
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2answers
87 views

Augmented Dickey-Fuller Unit Root Test & Cointegration

Using Stata 13. I have a pair of variables (x, y) over time. I want to regress y on x. Do I have to perform a ADF test 1st on x and y to find if both are stationary in their 1st difference (i.e. ...
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39 views

Regression with differenced variables

This is my data frame containing some interest rates as well as the amount outstanding of open market operations. Now I want to regress EurOis3 on ...
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1answer
50 views

Unit roots and order of differencing

I'm studying the stationarity with unit root tests and the order of integration in time series $\ln(x)$ and $\ln(y)$ found here. I'm using Dickey-Fuller test with constant but no trend. From what I ...
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60 views

Differencing variables with unit roots

I want to regress my dependent variable on my independent variables in R. First for the level of the variables: lm(y~x+z+u). Now since my variables are ...
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84 views

Is it ok to have a unit root within an independent variable?

The Dickey-Fuller and ADF tests testing for a unit root in variables are very sensitive. Some econometricians have personally indicated to me that in some cases it may be acceptable to model a ...
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2answers
73 views

Non-Stationary: Larger-than-unit root [duplicate]

I keep reading everywhere that a time series is non-stationary (e.g. http://en.wikipedia.org/wiki/Unit_root or http://en.wikipedia.org/wiki/Stationary_process) if there's a unit-root. But isn't a ...
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0answers
143 views

How to deal with unit roots in panel regression with fixed effects?

I am trying to figure out how to alter my panel regression in a case where fixed effects exists and one (or both) of the variables are I(1) processes (or in other words contain unit root). This is ...
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1answer
49 views

Difference between random walk and process integrated of order one?

I know that an $I(1)$ process becomes stationary after differencing once. However, I somehow always equated that to its being a random walk because say having a unit root process like \begin{eqnarray} ...
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2answers
56 views

unit-root test for unbalanced panel data

I have 146 institutions for 15 years. but all of them have not data for all time then I have unbalanced panel data. How can I examine uint-root test in stata or eviews? how can I define this ...
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99 views

Augmented Dickey-Fuller Trend and Intercept

I am trying to determine if I should include an "intercept" or a "trend and intercept" when using the Augmented Dickey-Fuller (ADF) test. I ran a regression with my dependent variable and a time ...
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31 views

Unit root and cointegration in Panel Data

What should I do when I found out that my variables are stationary in first differencies? Should I estimate model in differencies? How unit root is related with cointegration? Thx for answers.
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41 views

daily data series that exist seasonal component

I've a daily dataset(n=76), i try to find the best ARIMA model for forecasting purposes. When i check the correlogram (ACF), i found that there is a wave like pattern and this told me my data presence ...
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1answer
50 views

Unit Root testing and stationarity of a time series

I'm trying to understand: how is check for stationarity(or lack thereoff) linked to unit root testing. More so the logic of it. i understand the null hypothesis used in adf or kpss but I need the ...
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0answers
21 views

Large N, small T panel - modeling

I would like to ask your opinion on the possibility to use repeated survey results for panel data models. It is likely that at least some of the variables will be nonstationary. Is it necessary to ...
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1answer
172 views

Clarification on ARDL/Unrestricted Error Correction Model

I have a few questions about unrestricted error correction models. The UECM for a model where $Y$ is the dependent variable and $x$ is the sole independent variable is given by, $$ \Delta ...
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0answers
57 views

Regressing nonstationary on stationary variable

I am trying to empirically estimate the coefficient for the Okun's law as a relationship between output growth and unemployment. I am using the simple gap version, where I regress real output growth ...
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36 views

Stationarity at different confidence levels

Everyone! My question is, when looking for cointegration between two variables, I need to make sure that they are not stationary in levels. However, one of the variables is not stationary at the 5% ...
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1answer
1k views

Test for cointegration between two time series using Engle–Granger two-step method

I am seeking to test for cointegration between two time series. Both series have weekly data spanning ~3 years. I am trying to do the Engle-Granger Two Step Method. My order of operations follows. ...
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1answer
143 views

Best practice for ADF/KPSS unit root testing sequence?

I've been quite confused by the various unit root testing strategies recommended in the literature, so I was hoping others may have some advice on the best way to proceed using ADF and KPSS tests. ...
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65 views

Different results in ADF test

I have a question regarding the results I am getting from the augmented dickey fuller test for unit root. I am conducting the test in Eviews and I have the option to choose from intercept/trend and ...
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0answers
25 views

Unit Root Confirmed- How generate the new series with Diff, Trend,Intercept

I have a data series that became stationary at first difference and including both Trend and Intercept. I know how to generate a new variable using first differencing (Eviews) but how should I cater ...
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192 views

KPSS test in R interpretation

So in the R package tseries's kpss.test function, it seems I can specify whether the null hypothesis is trend stationary or level stationary(default). ...
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1answer
63 views

Structural-break unit-root test

My problem is the following: I have a model forecasting the sales of a certain brand. In period 4 a strike caused the sales to decrease. I want to know whether this strike has caused the sales to ...
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2answers
131 views

How to interpolate a variable with frequency of 5 years to annual data?

I have two time-series variables: each has 14 points with an interval of 5 years. The precise years are: ...
2
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1answer
1k views

How to read UNIT ROOT TEST results obtained from EVIEWS? I mean what values do we study to interpret our result?

Null Hypothesis: D(OIL_PRICES) has a unit root Exogenous: Constant Lag Length: 0 (Automatic - based on SIC, maxlag=22) ...
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76 views

Interpretation of results for unitroot test

Let's say I have a pure random walk: ...
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49 views

Unit root in shares

Suppose that dependent variable is a share of sth (for example it is a % of positive answers to the same question in each period of time t). If data shows the unit ...
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0answers
28 views

Unit Root Test and rolling data

Please could you kindly advise on the implication of testing for unit root (using the augmented dickey fuller approach) on rolling data. My feeling is that this wouldn't make much sense given the non ...
1
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1answer
162 views

Unit roots and GMM estimation

I want to estimate panel models of the following structure: $y_{it} = \rho y_{i,t-1} + \beta_1 x_1 + \dots + \beta_k x_k + c_i + \gamma_t + \epsilon_{it}$, where $c_i$ are time constant country ...
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50 views

Which type of random walk (1? 2? 3?) can unit root test?

Campbell (1997) showed that there are three types of random walk hypotheses classified by the level of restrictions on $\epsilon_t$: RW1 (random walk 1: increments are independent identically ...
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78 views

Time Series Econometrics: Cointegration methods for series with mixed degree of integration

I am performing a time series analysis on dataset ranging from 1974-2008. I have performed Augmented Dickey Fuller tests and Phillips Perron tests to check the stationarity/ order of integration of my ...
2
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1answer
1k views

Difference between series with drift and series with trend

A series with drift can be modeled as $y_t = c + \phi y_{t-1} + \epsilon_t$ where $c$ is the drift(constant), and $\phi=1$ A series with trend can be modeled as $y_t = c + \delta t + \phi y_{t-1} + ...
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619 views

Interpreting Augmented Dickey-Fuller in R

I know that this has been discussed before, but those discussions did not really answer my questions. I know how the ADF test works, but I am having trouble interpreting the output for the three ...
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0answers
76 views

Contradictory xtunitroot results

I am using unit root tests in Stata's xtunitroot command. The data are annual wage replacement rates for unemployment benefits in each of the 50 states for 1977 to 2006. (They vary noticably from ...
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49 views

Time series with an order of integration greater than 1

The issue of unit roots and what $ I(1) $ variables do to a regression estimation is covered clearly online. However, it is of course possible to have order of integration greater than 1. What does it ...
2
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1answer
353 views

How to conduct the Lluís Carrion-i-Silvestre et al. (2005) LM Unit Test and the non-linear ADF in Stata?

I am trying to test stationarity for a panel of 15 countries current account (1980–2012) annual data in Stata. I have chosen the LM unit root test by Lluís Carrion-i-Silvestre et al. (2005; to ...
2
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3answers
1k views

Augmented Dickey Fuller output conflicting in Stata

I am required to perform unit root testing on a given time series. The output obtained in Stata is somewhat confusing me. To the best of my knowledge I am obtaining two conflicting results, Stata ...
0
votes
1answer
280 views

If time series is tested for Unit Root by ADF, PP, KPSS,… which one is preferred?

If time series is tested for Unit Root, (by ADF, PP, KPSS,...) problem is detected with some tests and not found by others. which one is preferred? For example if ADF says us that Unit root is existed ...
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0answers
109 views

Augmented Dickey-Fuller test

I am now working with Stata and I found out I have a unit root in my regression. How can I correct for this, because I can read everywhere what the test does but if you have a unit root, what to do ...
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1answer
136 views
0
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1answer
128 views

Cointegrated series

My problem is this: I have 2 series $y$ and $x$ that I want to verify are cointegrated. So first I verified them with ADF unit root test and revealed that one variable is integrated at first ...
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0answers
471 views

Confusion about the term “stochastic drift”

After reading lots of material about the subject, I believe that the term "stochastic drift" is defined in a two different ways. These two different definitions make the term unambiguous and I assume ...