More economists think we're in a recession or on the verge of one. Yet the definition is vague:

"A recession is a significant decline in activity spread across the economy, lasting more than a few months, visible in industrial production, employment, real income and wholesale-retail trade."

That's according to the National Bureau of Economic Research (NEBR). When most analysts discuss stock performance during recessions — Citi Investment Research, for example, says the S&P 500 has dropped an average of 25.6 percent from its peak before a recession to its trough — they are using dates set by NBER.

The trouble is, this private, nonprofit group declares when recessions begin and end only after the fact. It didn't call the most recent recession, which began in March 2001, until November of that year. By then, the recession was already ending, though NBER wouldn't declare that until 2003.

Though many observers define a recession as two consecutive quarters of contraction in the economy, NBER takes a broader view. It says growth is "the single best measure" of economic health but looks at the depth of a contraction, not just the duration.

"It's more accurate to say that a recession — the way we use the word — is a period of diminishing activity rather than diminished activity," NBER says. The group also studies income and employment trends, which cover activity across the entire economy.

更多的經(jīng)濟(jì)學(xué)家認(rèn)為我們處在一個(gè)經(jīng)濟(jì)衰退時(shí)期，或至少是處在經(jīng)濟(jì)衰退的邊緣。但是經(jīng)濟(jì)衰退的定義還不是很明確：

“經(jīng)濟(jì)衰退是整體經(jīng)濟(jì)的活動明顯減退，持續(xù)幾個(gè)月以上，在工業(yè)生產(chǎn)，就業(yè)，實(shí)際收入和批發(fā)零售業(yè)方面表現(xiàn)明顯。”

這是依據(jù)美國國家經(jīng)濟(jì)研究局（NEBR)的說法.當(dāng)很多經(jīng)濟(jì)學(xué)家都在討論股票市場在經(jīng)濟(jì)衰退中的表現(xiàn)時(shí)－如花旗投資研究說，從經(jīng)濟(jì)衰退周期高峰時(shí)看，斯坦福五百種股票指數(shù)已經(jīng)平均下降25.6％－他們用的是NBER設(shè)定的周期。

這不是公開的，非盈利機(jī)構(gòu)聲稱，麻煩的是，經(jīng)濟(jì)衰退開始與結(jié)束都是在事實(shí)之后。最近的還不能稱之為經(jīng)濟(jì)衰退，從2001年3月開始，直到那年的11月。到那時(shí)，盡管NBER到2003年才宣布經(jīng)濟(jì)衰退已經(jīng)結(jié)束。

盡管許多觀察家定義經(jīng)濟(jì)衰退依靠兩個(gè)連續(xù)季度的經(jīng)濟(jì)萎縮，NBER看得更廣。它說經(jīng)濟(jì)增長是“最簡單最好的衡量”經(jīng)濟(jì)健康指標(biāo)，但是看的是衰退的深度，不是持續(xù)時(shí)間。

NBER稱：“更確切的說經(jīng)濟(jì)衰退－我們現(xiàn)在用這個(gè)詞－是一段時(shí)期經(jīng)濟(jì)活力減退，并不是失去活力”這個(gè)集團(tuán)也研究收入與就業(yè)趨勢，包括全面的經(jīng)濟(jì)活動。