Sources: Prior to 1917-Ansley Coale and Melvin Zelnik, New Estimates of Fertility and Population in the United States (Princeton: Princeton University Press, 1963). 1917 to 1968-U.S. National Center for Health Statistics, Natality Statistics Analysis,Series 21, Number 19, 1970. 1969 to 1971-U.S. Bureau of the Census, Current Population Reports, Series P-23, No. 36, "Fertility Indicators: 1970," 1971. The figure for 1971 is based on an unpublished Census staff estimate.