Are money and consumption additively separable in the euro area? A non-parametric approach

We propose a numerical test of the non-parametric conditions for additive separability between consumption and real money balances, building on Varian (1983). If additive separability is rejected, then real balances enter into the theoretical IS curve. We test whether or not monetary assets and consumption are additively separable for the euro area using quarterly data from 1991 to 2005. Previous results using a parametric approach suggest that real balances can be excluded from the IS curve. We find that additive separability is violated over this sample period. After 1992, however, violations involve only a few observations and are in some instances related to measurement problems in the data. Overall, our results tend to support the claim that perfect non-separability between consumption and real balances is implausible, but that non-separabilities may not be very important empirically. At the same time, we reject additive separability throughout if we extend the sample period back to the 1980s, a period characterised by higher volatility in inflation and money growth.