A parity progression ratios (PPR) is a measure commonly used in demography to study

fertility Fertility in colloquial terms refers the ability to have offspring. In demographic contexts, fertility refers to the actual production of offspring, rather than the physical capability to reproduce, which is termed fecundity. The fertility rate ...

. The PPR is simply the proportion of women with a certain number of children who go on to have another child. Calculating the PPR, also known as

a_x

, can be achieved by using the following

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

a_x = \text x+1 \text /\text x  \text

Hinde, A (1998) "Demographic Methods", Hodder Arnold Publication. In more

developed countries A developed country, or advanced country, is a sovereign state that has a high quality of life, developed economy, and advanced technological infrastructure relative to other less industrialized nations. Most commonly, the criteria for eval ...

where two-child families are seen as the norm

a_2

(or the proportion of women with two children who go on to have a third) is of critical importance in determining overall fertility levels.

a_0

is simply the proportion of women who become mothers.

References

{{Reflist Human pregnancy