Decomposing Fertility Rates in Australia: The Impact of changing relationship patterns and increasing singlehood

Most children are born to cohabiting or married parents, and being in a relationship is generally seen as a pre-requisite to childbearing. As such, total fertility can be thought of as being influenced by the proportion of the population that is partnered, and also the fertility behaviour of those in a partnership. In Australia, as in other countries, the proportion of the population of childbearing age that is single has increased over time. This paper examines how Australian fertility rates over the last three decades, from 1991 to 2019, have been affected by changing relationship patterns, and in particular the increasing rate of singlehood. Birth registration data, perinatal statistics and census data are used to investigate relationship trends as well as how childbearing has varied over time for women who are cohabiting, married or single. We find that while the contribution of marital fertility to the total fertility rate has decreased over time, while the contribution of cohabiting fertility has increased. Over the last few decades childbearing outside of partnerships has remained low, and concentrated in the younger age groups. Using decomposition analysis, we then separate changes in fertility into rate effects and a composition effect. We find that among partnered women there has been a shift in fertility rates from younger to older ages, but overall the fertility rate within relationships has remained relatively stable. However, the changing composition of women and the decline in the proportion who are partnered has had a negative contribution to fertility levels, particularly at the younger ages.