The children's ages in the census lists of the 3rd revision: the problem of data reliability and birth rate calculation

This article examines how the ages of serfs' children (0–17 years) in the Simbirsk Uyezd were recorded during the poll tax census (the 3rd revision), and which errors and distortions arose as illiterate informants estimated children's ages. Special attention is paid to the extent to which these factors affect the use of revision lists for reconstructing trends of birth rate. The region and social group were selected as the southern borderlands of the Middle Volga region were actively colonized in the mid-18th century involving landlords that organized large-scale migrations of their serfs. In the future studies, it makes possible to calculate the demographic effect of these migrations, including their impact on birth rate. As for the research methods, the author had built a database containing information on 12,952 male and female serfs who were resettled between the 2nd revision and the 3d revision to the southern part of Simbirsk Uyezd (Zavalny Stan). Then the accuracy of children's age was estimated using statistical techniques, including mean absolute error and sex-age pyramid. The study shows that different informants usually estimated the ages of the same children in a similar way, with an average error of about 0.5 year, substantially lower than that observed for adult women. At the same time, this consistency produced systematic age heaping around a limited set of ages (3, 5, 8, 10, 12 and 15 years), which significantly distorted annual crude birth rates. These preferred ages largely correspond to major stages of child maturation and labor socialization known from ethnographic studies of the Russian peasantry. The article concludes that age heaping of revision lists must be statistically smoothed to reconstruct trends of birth rate.