Some Cautions on the Use of Panel Methods for Integrated Series of Macro-Economic Data

We show how the use of panel data methods such as those proposed in single equations by Kao (1999) and Pedroni (1999) or in systems by Larsson and Lyhagen (1999) to investigate economic hypotheses such as purchasing power parity or the term structure of interest rates may be affected by the existence of cross-unit cointegrating relations. The existing literature assumes that such relations, that tie the units of the panel together, are not present. Using empirical examples from a panel of OECD countries we show that this assumption is very likely to be violated. Simulations of the properties of panel cointegration tests in the presence of cross-unit relations are then presented to demonstrate the serious cost of assuming away such relations. Some fixes are proposed as a way of dealing with these more general scenarios.