Testing for Non-Stationarity in Finance

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Questions and Answers

Why is testing for non-stationarity important in regression analysis?

  • Non-stationary variables have finite persistence of shocks, leading to accurate regression analysis.
  • Non-stationary variables can lead to spurious regressions with high R2 values, even if the variables are unrelated. (correct)
  • Stationary variables always lead to valid hypothesis tests about regression parameters.
  • Trending variables do not affect the validity of asymptotic analysis assumptions.

Which model characterizes non-stationarity as a random walk with drift?

  • $y_t = \mu + y_{t-1} + u_t$ (correct)
  • $y_t = \alpha + \beta t^2 + u_t$
  • $y_t = \mu + \frac{1}{2}y_{t-1} + u_t$
  • $y_t = \alpha + \beta t + u_t$

What happens to the standard assumptions for asymptotic analysis if the variables in a regression model are non-stationary?

  • The standard assumptions for asymptotic analysis will not be valid. (correct)
  • The standard assumptions for asymptotic analysis become more accurate.
  • The standard assumptions for asymptotic analysis will always hold true.
  • The standard assumptions for asymptotic analysis will lead to higher t-ratios.

What is the general form of an explosive process in the given context?

<p>$y_t = \mu + \phi y_{t-1} + u_t$ where $\phi &gt; 1$ (A)</p> Signup and view all the answers

What does a value of $\phi > 1$ indicate in the context of non-stationarity?

<p>Shocks to the system are not only persistent through time, but also propagated to have an increasingly large influence. (A)</p> Signup and view all the answers

What is required to induce stationarity in the case of deterministic non-stationarity?

<p>Detrending (C)</p> Signup and view all the answers

What is the characteristic of an I(2) series?

<p>It contains two unit roots and would require differencing twice to induce stationarity. (A)</p> Signup and view all the answers

What is the basic objective of testing for a unit root in time series?

<p>$\phi = 1$ (D)</p> Signup and view all the answers

What does an I(0) series indicate?

<p>It is a stationary series. (C)</p> Signup and view all the answers

What does an I(1) series indicate?

<p>It contains one unit root and would require differencing once to induce stationarity. (D)</p> Signup and view all the answers

What does an I(2) series indicate?

<p>It contains two unit roots and would require differencing twice to induce stationarity. (D)</p> Signup and view all the answers

What are the characteristics of I(0), I(1), and I(2) series?

<p>I(2) series contains two unit roots, I(1) series contains one unit root, and I(0) series is stationary. (A)</p> Signup and view all the answers

How do we generalize the concept of a non-stationary series?

<p>By considering the case where the series contains more than one 'unit root', requiring more than one application of the first difference operator, $\Delta$, to induce stationarity. (C)</p> Signup and view all the answers

Non-stationary series can lead to spurious regressions, where a regression of one variable on another could have a high R2 even if the two are totally unrelated.

<p>True (A)</p> Signup and view all the answers

The random walk model with drift is given by the equation $y_t = \mu + y_{t-1} + u_t$ where $u_t$ is an iid process.

<p>True (A)</p> Signup and view all the answers

If the variables in a regression model are not stationary, the standard assumptions for asymptotic analysis will not be valid, and the usual t-ratios will not follow a t-distribution.

<p>True (A)</p> Signup and view all the answers

There are two models frequently used to characterize non-stationarity: the random walk model with drift and the deterministic trend process.

<p>True (A)</p> Signup and view all the answers

An I(2) series contains two unit roots and so would require differencing twice to induce stationarity.

<p>True (A)</p> Signup and view all the answers

Detrending a stochastic non-stationary series involves differencing the series to induce stationarity.

<p>True (A)</p> Signup and view all the answers

The model $y_t = \mu + \phi y_{t-1} + u_t$ characterizes the non-stationarity as an explosive process when $\phi > 1$.

<p>True (A)</p> Signup and view all the answers

A series that is integrated of order $d$ is said to be $I(d)$.

<p>True (A)</p> Signup and view all the answers

If a non-stationary series $y_t$ must be differenced $d$ times before it becomes stationary, then it is said to be integrated of order $d$.

<p>True (A)</p> Signup and view all the answers

The basic objective of testing for a unit root in time series is to test the null hypothesis that $\phi = 1$ in the model $y_t = \phi y_{t-1} + u_t$.

<p>True (A)</p> Signup and view all the answers

An I(0) series is a non-stationary series that contains no unit roots and is already stationary.

<p>False (B)</p> Signup and view all the answers

If $\phi > 1$, shocks to the system are not only persistent through time, they are also propagated, leading to an increasingly large influence.

<p>True (A)</p> Signup and view all the answers

Consumer prices have been argued to have 2 unit roots, indicating a high degree of non-stationarity.

<p>True (A)</p> Signup and view all the answers

The majority of economic and financial series contain a single unit root, making them $I(1)$ series.

<p>False (B)</p> Signup and view all the answers

The second case, $yt = \mu + yt-1 + u_t$, is known as deterministic non-stationarity and requires detrending to induce stationarity.

<p>False (B)</p> Signup and view all the answers

The first difference operator, $\Delta$, is used to induce stationarity in a non-stationary series.

<p>True (A)</p> Signup and view all the answers

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