A Note on the Origin of the Net Reproduction Ratio.

The net reproduction ratio (NRR) is a useful measure of the growth of a population from one generation to the next. Like the expectation of life, it is based on a stable or Malthusian population and is not influenced by the actual population structure. Its use in this country was first advocated by Robert Kuczynski in the 1930s and, despite some reservations, it is still published for this and many other countries, particularly in the United Nations Demographic Yearbook. Kuczynski attributed its origin to Richard Boeckh, who, at the relevant time, around 1890, was Director of the Statistical Office of the City of Berlin. Boeckh discusses his data and the problems met. He estimates, for example, that two-ninths of all illegitimate children are subsequently legitimized by the marriage of their parents. In a census they are reported as legitimate, producing an inconsistency between census and registration data. He checks reliability, for example by showing that the decrease in the number of marriages with successive numbers of children is regular. At that time, no details of mother's age at birth were collected at registration in England. For this reason, Farr starts with Norwegian data as preferable to those from Scotland, Sweden or Denmark where this information was also available.