Darker bars mark wartime expansions. Based on duration, the changing nature of expansions is not quite as evident as for contractions. But of the 21 expansions prior to World War II, only three lasted more than three years. In contrast, of the 10 expansions since, only three have lasted less than three years. A simple comparison of the duration of expansions and contractions does suggest the U.S. economy has performed better in the post-World War II era.
Recessions are shorter, expansions are longer.
These changes strongly suggest that business cycles have changed over time. However, a simple comparison of duration cannot tell us about the severity of recessions or the strength of expansions. This would be better measured by the decline in output that occurs in a recession or the growth that occurs in an expansion. However, most studies that examine how volatile economic activity has been do conclude that output has been somewhat more stable in the post-World War II era. This conclusion, however, is not universally accepted.