Since the time of the Great Famine in 1847, the population of Ireland steadily decreased until the time of economic expansion in the 1960s. The principal causes of this decline were high emigration and low marriage rates due to a stagnant economy and large-scale unemployment. Ireland did not experience the demographic transition typical of most Western European countries in the post-World War II period. It was not until much later that Ireland manifested the characteristics of this transition, giving rise in the 1970s to a baby boom. The effects of this baby boom have been a major influence on Irish families since then, with Ireland having the youngest population in the European Union.
With an upsurge in the economy in the 1960s, birth rates increased. By 1971 the birth rate had reached a high of 22.7 per 1000 of population, giving a total period fertility rate of four, which is almost twice the replacement level. Since then, birth rates have declined, and by the 1990s they were below replacement level. By 2000 the birth rate had fallen to 14.3 and the total period fertility rate to 1.89 (Vital Statistics 2001). However, due to an increase in net immigration, largely because of the return of Irish workers and their families to take up employment in Ireland's new booming economy of the 1990s, the population continued to increase.
These changes were also accompanied by changes in marriage rates, age at time of marriage, age at the time of first maternity, family size, the number of out-of-wedlock births, marital separation, and cohabitation. By the end of the twentieth century Ireland had caught up with the demographic trends in most Western European countries and, apart from some differences, the overall pattern is much the same. The biggest difference is that while most of Europe experienced these changes over a period of two generations, Ireland went through them in one.