The analysis of marriage data has been neglected by demographers until a relatively late stage in the development of the subject. In the earlier stages of population study interest was focused on mortality, and the techniques for measuring mortality had been more or less perfected by the middle of the nineteenth century (Glass 1956). Deaths were studied by means of age-specific mortality rates, and it was to be expected that when the analysis of fertility became the centre of interest, similar techniques would be employed. Fertility rates were regarded as a function of the age distribution of the female population, and age-specific fertility rates, combined into gross and net reproduction rates, became the principal tool of replacement and fertility analysis. A number of the early students of fertility were biologists by training, or had a biological outlook, and so tended to stress biological rather than social influences on fertility. This method would be legitimate in societies in which all females marry or cohabit shortly after puberty and where no attempt is made to control fertility within marriage. Under those circumstances, the age distribution of the female population will be the primary and principal determinant of human fertility. However, in modern European countries it is no longer legitimate to study fertility in terms of female age distribution alone. In this country the bulk of reproduction takes place within marriage (legitimate births account for about 95% of all births), and though among the younger women marriage may not infrequently follow conception rather than precede it, even if pre-nuptial conceptions are excluded the proportion of maritally conceived births only falls to 87%. Moreover, given the small family system prevalent in this country to-day, the normal size of family may be achieved without much difficulty even by women who marry relatively late. The amount and timing of marriage is therefore important in the study of fertility and much greater attention has recently been devoted to the study of nuptiality. The Statistics Committee of the Royal Commission on Population, for instance, devoted much time to the study of marriage trends (Hajnal 1950).