Did the Catholics always have larger families?:
Religion, Wealth and Fertility in Rural Ulster before 1911

Cormac O'Grada's analysis of the marital fertility of farmers' and farm labourers' wives in rural Derry c. 1911 based on manuscript census material suggests that the well-known gap between Catholic and Protestant family size was present even then. The difference was quite small, however - about 0.3 children per completed family - and insignificant for women who had married before the mid-1880s. Various indicators of 'wealth' suggest that, all else equal, wealthier couples have more children, although there is also a tendency for labourers to have more children than farmers. Had Catholics in rural Derry been as well-off as their Protestant counterparts, they would have had more children. O'Grada's finding contrasts with the popular belief today that the larger families reared by northern Catholics reflect a culture of poverty.

Did the Catholics always have larger families?: Religion, Wealth and Fertility in Rural Ulster before 1911
Cormac O'Grada

Discussion Paper no. 6, February 1984 (HR)