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.

更多的經濟學家認為我們處在一個經濟衰退時期，或至少是處在經濟衰退的邊緣。但是經濟衰退的定義還不是很明確：

“經濟衰退是整體經濟的活動明顯減退，持續幾個月以上，在工業生產，就業，實際收入和批發零售業方面表現明顯。”

這是依據美國國家經濟研究局（NEBR)的說法.當很多經濟學家都在討論股票市場在經濟衰退中的表現時－如花旗投資研究說，從經濟衰退周期高峰時看，斯坦福五百種股票指數已經平均下降25.6％－他們用的是NBER設定的周期。

這不是公開的，非盈利機構聲稱，麻煩的是，經濟衰退開始與結束都是在事實之后。最近的還不能稱之為經濟衰退，從2001年3月開始，直到那年的11月。到那時，盡管NBER到2003年才宣布經濟衰退已經結束。

盡管許多觀察家定義經濟衰退依靠兩個連續季度的經濟萎縮，NBER看得更廣。它說經濟增長是“最簡單最好的衡量”經濟健康指標，但是看的是衰退的深度，不是持續時間。

NBER稱：“更確切的說經濟衰退－我們現在用這個詞－是一段時期經濟活力減退，并不是失去活力”這個集團也研究收入與就業趨勢，包括全面的經濟活動。