Human Science Explored

Prompted by the selection of the new Pope, I’ve been reflecting on Catholicism in Australia. The Catholic community within Australia has remained roughly steady in relative size over time, while other religious communities have grown or shrunk. To understand this better, I decided to take a look at the Australian census data for 2006 and 2011. By modelling aging over five years and factoring in known probabilities of death at different ages, I was able to compare the 2011 numbers against what might have been “expected.” This bar chart shows the resulting anomalies:

Not shown in this chart are 346,377 children under 5 as at 2011, who were either born in Australia, or who were part of immigrant families:

In addition to these babies, the chart shows that for ages 5–16 and 26–53 there is a net influx, due largely to immigration, of 193,000 Catholics. These figures are consistent with the fact that roughly 20% of immigrants are Catholic.

For ages 17–25, the chart shows a net outflow (after immigration) of 50,000 young people leaving the Catholic Church. The peak anomaly is at age 21 which, given the five-year period, corresponds to people leaving at age 18 or 19. The chart also shows smaller net outflows for ages 54 and up, but these probably reflect inaccuracies in my death-rate estimates, which are based on the Australian population as a whole.

The chart below summarises these factors, which led to an increase of the Catholic population from 5,126,883 to 5,439,267 over the period (a slight relative drop from 25.8% to 25.3% of the Australian population). Not reflected in these numbers is the equally interesting demographic shift towards non-Anglo-Celtic groups. The census data also allows that phenomenon to be explored, but that is beyond the scope of this blog post.

– Tony