A Note on the Pooling of Individual PANIC Unit Root Tests

One of the most cited studies in recent years within the field of nonstationary panel data analysis is that of Bai and Ng (2004, A PANIC Attack on Unit Roots and Cointegration. Econometrica 72, 1127-1177), in which the authors propose PANIC, a new framework for analyzing the nonstationarity of panels with idiosyncratic and common components. This paper shows that, although valid at the level of the individual unit, PANIC is not an asymptotically valid framework for pooling tests at the aggregate panel level.