⁹The out-of-sample period 2004-2007 was used to avoid endogeneity problems with the in-sample values of the state variables. The interregional trade flows data for Spain show a robust empirical regularity for the Spanish trade pattern (see Llano et al. 2010), demonstrating the existence for each Spanish region of stable relationships in terms of clients and suppliers. In essence, regional trade patterns do not change much over time.