1. Lutz, W., Sanderson, W. & Scherbov, S. Doubling of world population unlikely. Nature 387, 803–805 (1997).
2. United Nations. Long-Range World Population Projections: Based on the 1998 Revision (United Nations, New York, ESA/P/WP.153, 1999).
3. O'Neill, B. C., Scherbov, S. & Lutz, W. The long-term effect of the timing of fertility decline on population size. Pop. Dev. Rev. 25, 749–756 (1999).
4. US Census Bureau. International Database 10 May 200 edition 〈http://www.census.gov/ipc/www/worldpop.html〉 (US Census Bureau, 2000).
5. World Bank. World Development Indicators (CD-ROM) (World Bank, Washington DC, 2000).