The so-called Cauchy estimator uses the sign as instrument for the first lag in autoregressions, and the resulting t-type statistic has a standard normal distribution even in the unit root case. Thus, nonstandard asymptotics of the usual unit root tests such as the augmented Dickey-Fuller [ADF]...

Several panel unit root tests based on different ways to account for cross-unit dependence are reviewed. The note then illustrates the tests by checking whether the martingale difference hypothesis is appropriate for stock prices on the German stock market: according to the martingale difference...

We propose an IV panel unit root test robust to nonstationary error volatility. Its finite-sample performance is convincing even for many units and strong cross-correlation. An application to GDP prices illustrates the inferential impact of nonstationary volatility.