But, in a world of large short-term capital flows, central-banks’ policy interest rates – or even just announcements about likely future rates – also have a major impact. Moreover, quantitative easing affects exchange rates and trade, even if central banks purchase only domestic assets, as demonstrated by recent movements in the exchange rates of the dollar, the euro, and the yen.
各国财政部和央行可以通过各种机制抑制利率从而获得比较贸易优势，这让情况变得更加复杂了。最直接的办法是购买外国资产。但是，在短期资本流量巨大的世界中，央行的政策利率——甚至只是关于未来可能利率的声明——也能产生巨大影响。此外，量化宽松影响着汇率和贸易，即使央行只购买国内资产时也是如此，最近的美元、欧元和日元汇率走势就是明证。