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Notice to Readers: World's Population to Reach Six Billion

The United Nations (UN) estimates that the world's population will reach six billion on October 12, 1999 (1). The world's population reached one billion in 1804; subsequently, one billion increases came at intervals of 123, 33, 14, 13, and 12 years. Population growth rates increased over time because of high fertility rates and declines in mortality rates, especially since the early to mid-1900s. The UN projects that it will take 14 years for the world's population to reach 7 billion and another 15 years to reach 8 billion.

During 1995-2000, the world's population has grown at an annual rate of 1.3%. If this rate remains the same, the population will double in 52 years (2). This growth rate is substantially less than the peak growth rate of 2.0% during 1965-1970 and less than the rate of 1.5% during 1990-1995.

The decline in world population growth rates is a result of substantial declines in fertility in less-developed countries during the past 25 years. Overall, in developing countries, fertility declined by approximately one third between the 1960s and late 1980s, from an average of six children per woman to four per woman. This decline has continued into the 1990s.

Although other factors, such as the age of women at first marriage and induced abortion, help explain the fertility decline, the most important determinant of declining fertility in less developed countries is the increased use of effective contraception (3). An estimated 53% of all women of reproductive age in developed countries who are married or living in a consensual union are using some form of contraception; this rate is referred to as the contraceptive prevalence rate (CPR). In Latin America and the Caribbean, the CPR is 58%. In eastern Asia, excluding Japan but including China, the CPR is 79%. CPR is lowest in sub-Saharan Africa at 12%; however, in Botswana, Kenya, and Zimbabwe, CPR is 25%.


  1. United Nations. World population prospects--the 1998 revision, Vol. 1: comprehensive tables. New York: United Nations, 1999.
  2. Robey B, Rutstein S, Morris L, Blackburn R. The reproductive revolution: new survey findings. Baltimore, Maryland: The Johns Hopkins University Population Reports, 1992 (series M, no. 11).
  3. Westoff CF, Moreno L, Goldman N. The demographic impact of changes in contraceptive practice in third world populations. Pop Dev Rev 1989;15:91-106.

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