Generation X is the demographic cohort following the post–World War II baby-boom, representing a generational change from the baby boomers. Many researchers and demographers use dates which correspond to the fertility-patterns in the population. For Generation X, in the U.S. (and broadly, in the Western world), the period begins at a time when fertility rates started to significantly decrease, following the baby boom peak of the late 1950s, until an upswing in the late 1970s and eventual recovery at the start of the 1980s.