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.

更多的经济学家认为我们处在一个经济衰退时期，或至少是处在经济衰退的边缘。但是经济衰退的定义还不是很明确：

“经济衰退是整体经济的活动明显减退，持续几个月以上，在工业生产，就业，实际收入和批发零售业方面表现明显。”

这是依据美国国家经济研究局（NEBR)的说法.当很多经济学家都在讨论股票市场在经济衰退中的表现时－如花旗投资研究说，从经济衰退周期高峰时看，斯坦福五百种股票指数已经平均下降25.6％－他们用的是NBER设定的周期。

这不是公开的，非盈利机构声称，麻烦的是，经济衰退开始与结束都是在事实之后。最近的还不能称之为经济衰退，从2001年3月开始，直到那年的11月。到那时，尽管NBER到2003年才宣布经济衰退已经结束。

尽管许多观察家定义经济衰退依靠两个连续季度的经济萎缩，NBER看得更广。它说经济增长是“最简单最好的衡量”经济健康指标，但是看的是衰退的深度，不是持续时间。

NBER称：“更确切的说经济衰退－我们现在用这个词－是一段时期经济活力减退，并不是失去活力”这个集团也研究收入与就业趋势，包括全面的经济活动。