1950年至1990年，美國通脹衰退后的失業(yè)率將會在一年時間里較初始值平均下降32.4％，向自然失業(yè)率靠攏。如果這次美國的失業(yè)率也照這個路徑從2009年下半年時的頂峰開始下降，那么現(xiàn)在的數(shù)值就應該是8.3％，而不是8.9％。

　　不幸的是，2010年美國失業(yè)率的凈下降與就業(yè)人口占總?cè)丝诒戎氐纳仙翢o關(guān)系，所有失業(yè)率的下降都來自勞動力出勤率的降低。18個月以來，失業(yè)率從10.1％降了下來，但就業(yè)人口占總?cè)丝诒戎厥冀K徘徊在58.4％。要是那些雖然失業(yè)、但能夠找到工作的人積極地尋找工作而不是徹底離開就業(yè)市場，而那些擁有全職工作的人能夠繼續(xù)擁有他們的工作，情況說不定會好些。

　　如果用這一觀點來看1950年至1990年美國的衰退期，那么美國就業(yè)人口占總?cè)丝诘谋戎兀瑧撛谑I(yè)率高出自然水平的年份里年均增加0.23％。如果2009年以來美國的失業(yè)人口占總?cè)丝诒戎卣沾艘?guī)律變化，那么當前的比值應該是59.7％，而不是58.4％。要是果真如此，那我們現(xiàn)在就應該處于“朝氣美國”時期，而不是現(xiàn)在這種經(jīng)濟半死不活的狀態(tài)。

　　毫無疑問，這是衡量當下美國萎靡不振的失業(yè)復蘇勢頭的最好標準。這一標準與其他美國標準是一致的：從產(chǎn)出看，真實GDP年均增長率為2.86％，與美國經(jīng)濟的潛在的生產(chǎn)力增長率相差無幾，與其他發(fā)達國家（不管是日本還是歐洲）的經(jīng)驗也沒什么大區(qū)別。

　　事實上，與美國今日之窘境形成鮮明對比的，只有正在發(fā)展中的亞洲。在那里，真實GDP的增長及失業(yè)率的下降證明，經(jīng)濟正在經(jīng)歷穩(wěn)固的快速復蘇——治理通脹馬上就要成為宏觀經(jīng)濟的當務之急了。

　　美國今天的復蘇為什么與之前兩次的情形一樣，只能以低于自然水平的速度推進呢？一個顯而易見的假設是：復蘇的速度肯定與導致衰退的原因有所關(guān)聯(lián)。1990年之前衰退期出現(xiàn)的原因是美聯(lián)儲政策的改變——從“保持商業(yè)常態(tài)”轉(zhuǎn)向“對抗通脹”。美聯(lián)儲此舉造成流動性的擠出，扭曲了資產(chǎn)價格，使得大量建筑和其他形式的投資以及部分消費品的價格變得無法承受（從而也讓生產(chǎn)變得無利可圖）。由此而來的商品、服務以及勞動力的過剩，將會使通脹率水平降低。

　　不過，一旦美聯(lián)儲實現(xiàn)了其對抗通脹的目標，流動性擠出政策也就宣告結(jié)束了。資產(chǎn)價格和收入會回到常態(tài)。而所有危機前處于盈利狀態(tài)的企業(yè)也會再一次出現(xiàn)盈利。因此，從企業(yè)家的角度看，如何東山再起其實是再明顯不過的了：回到你原來的地方，做你原來做的事。

　　但是，最近的一次衰退后，事情卻發(fā)生了變化（變化其實從之前兩次衰退后就開始了，但程度沒有這次這么徹底）。這次衰退出現(xiàn)的原因并非流動性擠出，因此美聯(lián)儲也就無法收起魔法棒讓資產(chǎn)價格回到衰退前的狀態(tài)。這意味著企業(yè)家問題變得要復雜很多，因為東山再起不再是恢復原先盈利的產(chǎn)品生產(chǎn)就行了，而是需要找到未來生產(chǎn)什么才能盈利。

　　經(jīng)濟學家丹·庫恩說，衰退就像是有人朝你的拼圖游戲踢了一腳，踢散了你的拼圖，有幾塊還翻了過去。過去美聯(lián)儲結(jié)束流動性擠出政策，能夠?qū)⒎^去的拼圖塊又翻回來。但現(xiàn)在的情況，卻是沒人能將拼圖正確地翻轉(zhuǎn)回來，因此要糾正就變得相當艱難。

　　事實上，我認為情況甚至要更糟。由于總需求一直萎靡不振，我們甚至不知道哪幾塊拼圖是正面朝上的。在正常產(chǎn)能利用率和失業(yè)率水平上具有很高生產(chǎn)率和盈利能力的新投資、商業(yè)貸款以及員工-企業(yè)匹配，如今卻都變得虧本了。

　　因此，美國現(xiàn)在需要做的不僅僅是重振需求，還要調(diào)整結(jié)構(gòu)。不幸的是，只靠市場自身無法創(chuàng)造需求復蘇，而在需求復蘇走上正軌之前，市場也無法進行結(jié)構(gòu)性調(diào)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.