衰退的形态
衰退的形态是指经济学家们用来描述衰退类型的用语。这些用语还没有特定的学术上的分类；可以说，是非正式的，随手拿过来的说法，用之于说明衰退和复苏的特性。
最常用的术语有V型、U型、W型、L型衰退。V，W，U，L的名称来自线性经济数据图表中曲线所形成的大概形状。这些字母同样也可以用来描述经济复苏的形态。
V型衰退
V型衰退，经济经受到急剧的衰落，但是，在很短暂时期中，又重新出现强烈的回升，于是在经济指标的图标上会形成一个明显的低谷，然后就会出现强烈的回升。根据宏观经济顾问们的说法，V型是经济衰退最常有的形态：经济复苏的力量与此前的急剧衰退历来会形成一个“急速反弹”的关系。因此，衰退和其复苏往往会形成一个V字形的轨迹。
最明显的V型衰退例子是1953年的美国经济衰退。1950年代初，美国经济蓬勃发展，但是美国联邦储备委员会以提高利率来造成通货膨胀，促使其衰退。1953年，增长减慢，到第三季度，经济萎缩2.4%，到第四季度，经济萎缩至6.2%，1954年第一季度，经济又萎缩2%，然后就开始回升，到1954年第四季度，经济增长达到了8%，回到了原先的水平。这样，在这一期经济衰退中，GDP形成了一个明显的V字形。
U型衰退
U型衰退的时期要比V型衰退时间长，其低谷曲线也没有V型衰退的低谷那么明显。GDP要有好几个季度的收缩，然后才会缓缓地回升到原先的增长趋势。国际货币基金会的前首席经济师西蒙·约翰森(Simon Johnson)说，U型衰退就像是个浴盆：你进去了，你会待在里面。侧面是滑溜溜的。也许底部还有些凹凸不平，但是你会有好长一段时间待在这浴缸里。美国1973-75年的经济衰退被认为是典型的U型衰退。在1973年，经济开始萎缩，并持续衰落了将近有两年时间。在底部跌跌撞撞了一段时间，到1975年，才开始复苏回升。
W型衰退
W型衰退也叫双下沉衰退，经济出现衰退后，会有一个短期的回升，但是很快又掉向低谷，这样的衰退，称为W型衰退。
美国1980年初出现的经济衰退就是W型衰退的实例。国际经济研究局认为，1980年代初出现了两次衰退。1980年1月至7月，经济出现衰退，从4月到6月，以年衰退率8%的速度萎缩。然后经济又进入一个快速增长的过程，在1981年的头三个月，经济以年增长率8.4的速度增长。但是保尔·伏尔克（Paul Volcker)领导下的美国联邦储备委员会采取提高利率的方式来防止通货膨胀，导致1981年7月至1982年11月间经济又跌向衰退的低谷（出现双下沉）。然后，在80年代随后的几年中，进入一个相当稳健的增长期。
L型衰退
L型衰退是经济一旦陷进一个严重的衰退，便一蹶不振连续许多年都无法见到增长的势头。一步跌落之后，随之是一条平线，使线形像个字母“L”的形状。这是经济衰退中最严重和最糟糕的形态。
L型衰退的典型实例是日本1990年随着资产价格泡沫的破裂而出现的经济衰退。自从二次大战以后，直到1980年代，日本的经济一直蓬勃增长。1980年代，日本发展出庞大的资产泡沫。泡沫破裂以后，经济出现大萧条，然后经济发展经历了许多年的迟缓状态，再也无法回复到1950-1990年代的高速增长的水平。美国2000年末期的经济衰退也同样是随着经济泡沫（美国的住房泡沫）而形成的，因此，有些经济学家担心美国即便在经济复苏以后，也还有可能会陷入一个延长的低增涨期中。
Recession shapes
Recession shapes are used by economists to describe different types of recessions. There is no specific academic theory or classification system for recession shapes; rather the terminology is used as an informal shorthand to characterize recessions and their recoveries.
The most commonly used terms are V-shaped, U-shaped, W-shaped, and L-shaped recessions. The shapes take their names from the approximate shape economic data make in graphs during recessions. The letters can also be applied referring to the recoveries (ie "V-shaped recovery").
V-shaped recession
V-shaped recession, the economy suffers a sharp but brief period of economic decline with a clearly defined trough, followed by a strong recovery. According to Macroeconomic Advisors, V-shapes are the normal shape for recession: "There is a strong historical “snap back” relationship between the strength of economic recovery and the severity of the preceding recession. Thus, recessions and their recoveries have a tendency to trace out a “V” shape."
A clear example of a v-shaped recession is the Recession of 1953 in the United States. In the early 1950s the economy in the United States was booming, but because the Federal Reserve expected inflation it raised interest rates, tipping the economy into recession. In 1953 growth began to slow, in the third quarter, the economy shrank by 2.4 percent. In the fourth quarter the economy shrank by 6.2 percent, and in the first quarter of 1954 it shrank by 2 percent before returning to growth. By the fourth quarter of 1954, the economy was growing at an 8 percent pace, well above the trend. Thus GDP growth for this recession forms a classic v-shape.
U-shaped recession
A U-shaped recession is longer than a V-shaped recession, and has a less-clearly defined trough. GDP may shrink for several quarters, and only slowly return to trend growth. Simon Johnson, former chief economist for the International Monetary Fund, says a U-shaped recession is like a bathtub: "You go in. You stay in. The sides are slippery. You know, maybe there's some bumpy stuff in the bottom, but you don't come out of the bathtub for a long time."
The Recession of 1973–75 can be considered a U-shaped recession. In early 1973 the economy began to shrink and continued to decline or have very low growth for nearly two years. After bumping along the bottom, the economy climbed back to recovery in 1975.
W-shaped recession
A W-shaped recession or "double dip" recession, occurs when the economy has a recession, emerges from the recession with a short period of growth, but quickly falls back into recession.
The Early 1980s recession in the United States is cited as an example of a W-shaped recession. The National Bureau of Economic Research considers two recessions to have occurred in the early 1980s.[4] The economy fell into recession from January 1980 to July 1980, shrinking at an 8 percent annual rate from April to June of 1980. The economy then entered a quick period of growth, and in the first three months of 1981 grew at an 8.4 percent annual rate. As the Federal Reserve under Paul Volcker raised interest rates to fight inflation, the economy dipped back into recession (hence, the "double dip") from July 1981 to November 1982. The economy then entered a period of mostly robust growth for the rest of the decade.
L-shaped recession
An L-shaped recession occurs when an economy has a severe recession and does not return to trend line growth for many years, if ever. The steep drop, followed by a flat line makes the shape of an L. This is the most severe of the different shapes of recession.
A classic example of an L-shaped recession occurred in Japan following the bursting of the Japanese asset price bubble in 1990. From the end of World War II throughout the 1980s, Japan's economy was growing robustly. In the late 1980s a massive asset-price bubble developed in Japan. After the bubble burst the economy suffered from deflation, and experienced years of sluggish growth; never returning to the higher growth Japan experienced from 1950-1990. Because the Late-2000s recession in the United States followed a similar economic bubble (the United States housing bubble) some economists fear the U.S. economy could enter a prolonged period of low growth even after recovering from the recession.
