1950年至1990年，美国通胀衰退后的失业率将会在一年时间里较初始值平均下降32.4％，向自然失业率靠拢。如果这次美国的失业率也照这个路径从2009年下半年时的顶峰开始下降，那么现在的数值就应该是8.3％，而不是8.9％。

　　不幸的是，2010年美国失业率的净下降与就业人口占总人口比重的上升毫无关系，所有失业率的下降都来自劳动力出勤率的降低。18个月以来，失业率从10.1％降了下来，但就业人口占总人口比重始终徘徊在58.4％。要是那些虽然失业、但能够找到工作的人积极地寻找工作而不是彻底离开就业市场，而那些拥有全职工作的人能够继续拥有他们的工作，情况说不定会好些。

　　如果用这一观点来看1950年至1990年美国的衰退期，那么美国就业人口占总人口的比重，应该在失业率高出自然水平的年份里年均增加0.23％。如果2009年以来美国的失业人口占总人口比重照此规律变化，那么当前的比值应该是59.7％，而不是58.4％。要是果真如此，那我们现在就应该处于“朝气美国”时期，而不是现在这种经济半死不活的状态。

　　毫无疑问，这是衡量当下美国萎靡不振的失业复苏势头的最好标准。这一标准与其他美国标准是一致的：从产出看，真实GDP年均增长率为2.86％，与美国经济的潜在的生产力增长率相差无几，与其他发达国家（不管是日本还是欧洲）的经验也没什么大区别。

　　事实上，与美国今日之窘境形成鲜明对比的，只有正在发展中的亚洲。在那里，真实GDP的增长及失业率的下降证明，经济正在经历稳固的快速复苏——治理通胀马上就要成为宏观经济的当务之急了。

　　美国今天的复苏为什么与之前两次的情形一样，只能以低于自然水平的速度推进呢？一个显而易见的假设是：复苏的速度肯定与导致衰退的原因有所关联。1990年之前衰退期出现的原因是美联储政策的改变——从“保持商业常态”转向“对抗通胀”。美联储此举造成流动性的挤出，扭曲了资产价格，使得大量建筑和其他形式的投资以及部分消费品的价格变得无法承受（从而也让生产变得无利可图）。由此而来的商品、服务以及劳动力的过剩，将会使通胀率水平降低。

　　不过，一旦美联储实现了其对抗通胀的目标，流动性挤出政策也就宣告结束了。资产价格和收入会回到常态。而所有危机前处于盈利状态的企业也会再一次出现盈利。因此，从企业家的角度看，如何东山再起其实是再明显不过的了：回到你原来的地方，做你原来做的事。

　　但是，最近的一次衰退后，事情却发生了变化（变化其实从之前两次衰退后就开始了，但程度没有这次这么彻底）。这次衰退出现的原因并非流动性挤出，因此美联储也就无法收起魔法棒让资产价格回到衰退前的状态。这意味着企业家问题变得要复杂很多，因为东山再起不再是恢复原先盈利的产品生产就行了，而是需要找到未来生产什么才能盈利。

　　经济学家丹·库恩说，衰退就像是有人朝你的拼图游戏踢了一脚，踢散了你的拼图，有几块还翻了过去。过去美联储结束流动性挤出政策，能够将翻过去的拼图块又翻回来。但现在的情况，却是没人能将拼图正确地翻转回来，因此要纠正就变得相当艰难。

　　事实上，我认为情况甚至要更糟。由于总需求一直萎靡不振，我们甚至不知道哪几块拼图是正面朝上的。在正常产能利用率和失业率水平上具有很高生产率和盈利能力的新投资、商业贷款以及员工-企业匹配，如今却都变得亏本了。

　　因此，美国现在需要做的不仅仅是重振需求，还要调整结构。不幸的是，只靠市场自身无法创造需求复苏，而在需求复苏走上正轨之前，市场也无法进行结构性调整。

　　Between 1950 and 1990 – the days of old-fashioned inflation-fighting downturns engineered by the United States Federal Reserve – America’s post-recession unemployment rate would fall on average 32.4% over the course of a year from its initial value toward its natural rate. If the US unemployment rate had started to follow such a path after peaking in the second half of 2009, it would now stand at 8.3%, rather than 8.9%.

　　Unfortunately, none of the net reduction in the US unemployment rate over the past year came from increases in the employment-to-population ratio; all of it came from declining labor-force participation. Unemployment has fallen from 10.1% over the course of the past 18 months, but the employment-to-population ratio has remained stuck at 58.4%. Perhaps it would be better if unemployed people who could have jobs – and who at full employment would have them – were actively looking for work rather than out of the labor force completely.

　　If you take that view, between 1950 and 1990, the US employment-to-population ratio would rise an extra 0.227% annually on average for each year that the unemployment rate was above its natural rate. If the US employment-to-population ratio had started to follow such a path after its 2009 peak, the current ratio would be 59.7%, rather than 58.4%. (In that case, we would be experiencing “morning in America,” rather than the current state of economic malaise.)

　　This is, I think, the best metric to use to quantify the decidedly sub-par pace of today’s jobless recovery in the US. It is not out of line with other American yardsticks: since the output trough, real GDP has grown at an average rate of 2.86%/year, barely above the rate of growth of the US economy’s productive potential. And it is not out of line with the experience of other rich economies, whether Japan or in Europe.

　　Indeed, today’s US predicament contrasts sharply only with the current experiences of developing Asia. There, real GDP growth and declining unemployment show a solid, well-entrenched, and rapid recovery – to the point that inflation will soon become a more significant macroeconomic problem than job creation.

　　The obvious hypothesis to explain why the current US recovery – like the previous two – has proceeded at a sub-par pace is that the speed of any recovery is linked to what caused the downturn. A pre-1990 recession was triggered by a Fed decision to switch policy from business-as-usual to inflation-fighting. The Fed would then cause a liquidity squeeze and so distort asset prices as to make much construction, sizable amounts of other investment, and some consumption goods unaffordable (and thus unprofitable to produce). The resulting excess supply of goods, services, and labor would cause inflation to fall.

　　As soon as the Fed had achieved its inflation-fighting goal, however, it would end the liquidity squeeze. Asset prices and incomes would return to normal. And all the lines of business that had been profitable before the downturn would become profitable once again. From an entrepreneurial standpoint, therefore, recovery was a straightforward matter: simply pick up where you left off and do what you used to do.

　　After the most recent US downturn, however (and to a lesser extent after its two predecessors), things have been different. The downturn was not caused by a liquidity squeeze, so the Fed cannot wave its wand and return asset prices to their pre-recession configuration. And that means that the entrepreneurial problems of are much more complex, for recovery is not a matter of reviving what used to be profitable to produce, but rather of figuring out what will be profitable to produce in the future.

　　As the economist Dan Kuehn likes to say, a recession is like somebody knocking your jigsaw puzzle, disturbing the pieces, and turning some of them over. When the Fed ends a liquidity squeeze, it turns the pieces right side up. So it is easy to reassemble the puzzle. Now, however, there is no one to turn the pieces right side up, so things are much harder to correct.

　　Indeed, I believe that things are even worse: as long as aggregate demand remains low, we cannot even tell which pieces are right side up. New investments, lines of business, and worker-firm matches that would be highly productive and profitable at normal levels of capacity utilization and unemployment are unprofitable now.

　　So, what America needs now is not just a recovery in demand, but also structural adjustment. Unfortunately, the market cannot produce a demand recovery rapidly by itself. And it cannot produce structural adjustment at all until a demand recovery is well under way.

　　J. Bradford DeLong, a former US Assistant Secretary of the Treasury, is Professor of Economics at the University of California at Berkeley and a Research Associate at the National Bureau for Economic Research.