Amid the hubbub over a few less-bad-than-expected statistics, America’s economic debate has turned to the nature of the recovery. Optimists expect a vigorous rebound as confidence returns, pent-up demand is unleashed and massive government stimulus takes effect. Most observers are bracing for a long slog, as debt-laden consumers rebuilt their savings, output growth remains weak and unemployment continues to rise. There is, however, something that eventually will have a much bigger impact on Americans’ prosperity than the slope of the recovery. That is the effect of the crisis on America’s potential rate of growth itself.

An economy’s long-term speed limit ( its “trend ”or “potential” rate of growth ) is the pace at which GDP can expand without affecting unemployment and, hence, inflation. It is determined by growth in the supply of labor along with the speed with which productivity improves. The pace of potential growth helps determine the sustainability of everything from public debt to the prices of shares. Unfortunately, the outlook for America’s potential growth rate was darkening long before the financial crisis hit. The IT-induced productivity revolution, which sent potential output soaring at the end of the 1990s, has waned. More important, America’s labor supply is growing more slowly as the population ages, the share of women working has leveled off and that of students who work has fallen.

由于一小部分经济数据显示当前经济状况并没有预期的那样坏，一些人就骚动起来，开始讨论起美国经济的复苏之路。乐观人士认为在信心恢复、压抑已久的内需得到释放和大量的政府刺激计划奏效的背景下，将会有一个强势的反弹。大多数专家，正准备迎来一个更加漫长的艰难之旅：债务累累的消费者正在重建他们的积蓄，产量的增长依旧迟缓，失业率仍在攀升……但是，还有一个比复苏趋势更会影响美国繁荣的东西，那就是这次危机给美国潜在的经济增长所带来的不良影响。

一个经济体长期处在最高的增长速度，是以GDP的增长不被失业率和通货膨胀所影响为条件的。而这，决定于劳动力供应的增长和生产力发展的速度。潜在增长的速度帮助决定了从国债到股价这一切能否持续稳定。遗憾的是，在金融危机发生很久以前，美国经济潜在增长率的前景就十分暗淡。IT行业引发的生产力革命，曾在上世纪90年代末使产量大幅上涨，但衰败了。更重要的是，美国劳动力供给的增长速度正变得比人口老龄化速度慢，女性工作者的比例已经稳定，学生的已经下降。