There are about 25 leading indicators that both change and predict future fertility and population. UN projections do not directly consider the future influence of these 25 leading indicators, but instead extrapolate recent population trends into the future. The leading indicators all have operated and seem to be continuing to operate to decrease future fertility. Since the leading indicators and the reduced fertility they cause and predict have not been considered by the UN, all past UN population projections for times more than 25 years in the future have been high. The low-variant projection has been by far the most accurate UN projection for times more than 25 years in the future, so the low variant will be used in this article.
Fertility rate is the total number of children born to the average woman.
A fertility rate of 2.1 is necessary to maintain population. Fear of vast population increase is the reason given for the UN Population Conference. World fertility and birth rates have been declining since 1955. No region's or country's population growth has been caused by increased birth rates. World population growth is mostly caused by the decline in the death rate.