During the Irish famine of 1846-1851 there were an estimated 1.0 million excess deaths, the migration of 1.3 million persons, and 300,000 averted births. To assess the influence of population changes at the local level in Ulster, decennial census records were analyzed for the Barony of Upper Ards, County Down, from 1841 to 1911. Data on marriages contracted in the four Roman Catholic, five Presbyterian, and eight Episcopalian congregations also were abstracted from civil parish registers for the period 1840-1915 and were used to calculate levels of random and nonrandom inbreeding through time by isonymy analysis. In the prefamine census of 1841 the total population of the Upper Ards was 16,964. From 1841 to 1911 population numbers decreased by 44.5%, with a consistent surplus of females in all parishes throughout the study period. Both population density and the number of persons per dwelling declined at equivalent rates, resulting in increasingly dispersed patterns of settlement. There was a marked overall increase in nonrandom inbreeding (Fn) in the immediate postfamine period, which was sustained throughout the nineteenth century before declining during 1900-1915. However, significant heterogeneity was observed in the Fn values calculated, both between and within each of the three main religious denominations, indicating differential local responses to marriage partner choice in the postfamine years. The observed changes are not compatible with a simple model of reduction in mate availability under conditions of population decline. Instead, they can most convincingly be explained in terms of a specific population response to the subsistence crisis initiated by the famine.
Bittles, A. H., & Smith, M. T. (1994). Religious differentials in postfamine marriage patterns, Northern Ireland, 1840-1915. I. Demographic and isonymy analysis. Human Biology, 66(1), 59-76.