[LINK] "Has the world reached replacement rate fertility?"

[rfmcdonald]

Over at Demography Matters, co-blogger Aslak takes on the common knowledge that replacement-rate fertilty--the number of children that an average woman in a society must have in order prevent population decline-- is 2.1. That, he points out, is a mistake.

At first glance, the question might seem odd, given that the global fertility rate is currently estimated by the UN to be somewhere around 2.5, well above 2.1, which is usually cited as the replacement rate. However, 2.1 is a number that is often bandied about somewhat lazily, even by people who should know better. It is important to remember that the replacement rate is not a constant and the 2.1 number is only really relevant for developed countries where the actual replacement rate is usually in the 2.06-2.08 range.

Three factors--age-specific fertility rates, female mortality rates and sex ratio at birth--play a huge role in determining replacement fertility. In some unfortuante countries, replacement fertility can be almost as high as 4!