NOTES: Data are based on births adjusted for underregistration for 1950 and on registered births for all other years. Starting with 1970 data, births to persons who were not residents of the 50 states or the District of Columbia are excluded. Birth data for Alaska and Hawaii have been included since 1959 and 1960, respectively. Starting with Health, United States, 2003, rates for 1991–1999 were revised using intercensal population estimates based on the 1990 and 2000 censuses. Rates for 2000 were based on bridged-race April 1, 2000, census counts. Starting with Health, United States, 2012, rates for 2001–2009 were revised using intercensal population estimates based on the 2000 and 2010 censuses. Rates for 2010 were based on bridged-race April 1, 2010, census counts. Rates for 2011 and beyond are computed using 2010-based postcensal estimates. See Appendix I, Population Census and Population Estimates. Some estimates have been revised and differ from previous editions of Health, United States. Data for additional years are available in the Excel spreadsheet version of this table on the Health, United States website at: https://www.cdc.gov/nchs/hus/index.htm.