Variables The data consists of rates, given for each calendar year. The fertility rates are per 1000 ever-married females by single years of age for ages 15 to 49. The data was derived by matching vital statistics on births with data on population exposed to risk, which came in part from population censuses and in part form intercensal estimation. Please note: this study does not include information on named individuals and would therefore not be useful for personal family history research.