Members of Generation Z are slightly less likely to be foreign born than Millennials; the fact that more American Latinos were born in the U.S. rather than abroad plays a role in making the first wave of Generation Z appear better educated than their predecessors. However, researchers warn that this trend could be altered by changing immigration patterns and the younger members of Generation Z choosing alternate educational paths. As a demographic cohort, Generation Z is smaller than the Baby Boomers and their children, the Millennials. According to the U.S. Census Bureau, Generation Z makes up about one quarter of the U.S. population, as of 2015. Provisional data from the Center for Disease Control and Prevention reveal that U.S. fertility rates have fallen below the replacement level of 2.1 since 1971. (It was 1.765 in 2017.) There was an 'echo boom' in the 2000s, which certainly increased the absolute number of future young adults, but did not significantly change the relative sizes of this cohort compared to their parents.