摘要：The question of whether migration can be an equilibrating force in the labour market is an important criterion for an optimal currency area. It is of particular interest currently in the context of high and rising levels of labour market disparities, in particular within the Eurozone where there is no exchange - rate mechanism available to play this role. We shed some new light on this question by comparing pre - and post - crisis migration movements at the regional level in both Europe and the United States, and their association with asymmetric labour market shocks. We find that recent migration flows have reacted quite significantly to the EU enlargements in 2004 and 2007 and to changes in labour market cond itions, particularly in Europe. Indeed, in contrast to the pre - crisis situation and the findings of previous empirical stud ies, there is tentative evidence that the migration response to the crisis has been considerable in Europe , in contrast to the United States where the crisis and subsequent sluggish recovery were not accompanied by greater interregional labour mobility in reaction to labour market shocks . Our estimates suggest that, if all measured population changes in Europe were due to migration for employment purposes – i.e. an upper - bound estimate – up to about a quarter of the asymmetric labour market shock would be a bsorbed by migration within a year. However, in the Eurozone the reaction mainly stems from migration of third - country nationals. Even within the group of Eurozone nationals, a significant part of the free mobil ity stems from immigrants from third countrie s who have taken on the nationality of their Eurozone host country
