On Wicksell’s definition – the best, and, in fact, the only definition I know of – the market interest rate was, if anything, above the natural interest rate in the early 2000’s: the threat was deflation, not accelerating inflation. The natural interest rate was low because, as the Fed’s current chairman Ben Bernanke explained at the time, the world had a global savings glut (or, rather, a global investment deficiency).
依据维克塞尔的定义，（这个定义是最好的，实际上也是我唯一所知的。）在本世纪早期，市场利率只能算是高于自然利率水平：当时的威胁是通货紧缩，而不是不断加速的通货膨胀。自然利率之所以低，是因为正如美联储现任主席本·贝南克当年解释的那样，世界正面对全球性储蓄过剩（或者说全球性投资匮乏。）