The reason for the growth of the Catholic population in Ulster is due to two things, one is that the Catholic population has traditionally had a higher birth rate than non Catholics, the other is that the emigration rate among Catholics in Ulster is far lower than the emigration rates for Catholics in the Irish Republic.
Ironically in the event of a United Ireland assuming that the emigration rates would rise to the same level as the rest of the Republic the Catholic population would shrink to the levels of the 1920's.
The reason for the lower emigration levels in Ulster is because the state is the biggest employer of Catholics and protestants with average salaries higher in the public sector than the private sector.
Even in the event of a Catholic majority a United Ireland is not guaranteed as it has been estimated that almost 30 per cent of Catholics would vote to retain the Union in any referendum.
