Some effects are already visible in a high degree of economic integration between the current Member States and the acceding countries. Lower trade costs and an increase in competition associated with the enlargement of the Single Market can have a significantly positive impact on growth in the European economy as a whole.
But the side effect might be, again, a somewhat diminished ability to extrapolate statistical patterns seen in the past to forecast the future, at least for some time. One notable source of dynamics in structural relationships, looking forward, will be the convergence across income and productivity levels.