Parity progression ratio

Definition

The term parity progression ratio (PPR) is typically used in the context of a cohort of females (such as a birth cohort) that has completed its childbearing years. Given such a cohort, and a nonnegative integer $i$, the parity progression ratio from birth order $i$ to birth order $i+1$ is defined as the ratio of the completed cohort fertility for that cohort for birth order $i+1$, to the completed cohort fertility for that cohort for birth order $i$.

Alternatively, the PPR describes the probability that a person in that cohort who has had $i$ children will proceed to have an $(i+1)^{th}$ child.