Brendan HalpinI'm looking at Irish population estimates (for a project on fertility) and this popped out. How female cohort size changes between 15-45, for cohorts from 1961. It tells quite a story.
At this age range change in cohort size is mostly due to migration. For cohorts between 1961 and 1978, there is a long stable pattern of cohort decline (emigration), well into the 1990s. But then everything changes. First the Celtic Tiger seems to have staunched emigration, and then with EU accession of the eastern European countries, there is substantial net in-migration.
Until the 2008/9 financial crisis, at least. Just before we have some very steeply rising cohort sizes, followed by a very sharp drop. But not for all cohorts. The sharpest rises and falls both seem to be for quite young cohorts, and older cohorts don't budge too much. There was huge reverse migration of eastern Europeans (and renewed emigration) but it seems very age sensitive: mostly younger adults, unattached.
Graph w/ added colour for the 66/76-2006 cohorts:
So there is sharp reverse-migration and emigration for some cohorts. Older cohorts don't change: harder to move if you're more settled, native or immigrant.
Since then, there was a period of some stasis but for the final 5-10 years we're seeing cohorts growing again, as inward migration returns.
I really like cohort perspectives. They can be very revealing.