<Li> Japan 1947--1949, 1971--1974 </Li> <P> In some of these examples, an "echo boom" followed some time after as the offspring of the initial boom gave rise to a second increase, with a baby "bust" in between . The birth years of the baby boom as noted being both short and long lived, creates what many believe to be a myth to the notion of defining baby boomers as one "generation", as a unified concept is clearly not possible . Indeed, multiple generations may be present in a single country such as Ireland where the boom lasted 36 years . This overlapping effect of generations is not illuminated when considering crude fertility rates . The only common ground for the collective boom is the same approximate starting year . This example can be applied to each state in the United States on an individual basis . The states with a census in place in 1946 saw fertility rates drop to pre-war levels throughout the 1960s, with the average being in 1964 . </P>

When did the baby boom take place in the united states