A study of 19th century French demographics using collaborative genealogy data.

Summary In the digital age, data can be collected massively, in a collaborative way and at a lower cost. Genealogy websites are flourishing on the Internet, offering their users the opportunity to reconstruct their family tree online. The work of collection and data entry done by these users can potentially be reused in historical demography to complete the knowledge of our ancestors' past. In our study, we use records concerning 2,457,450 French individuals or individuals of French origin who lived in the 19th century. First, we study the quality of these data. We highlight the presence of important biases, notably concerning the gender of individuals. Women are under-represented in the data compared to men. Biases related to fertility are also observed. Despite these limitations of collaborative genealogy data, we show in a second step that it is possible to find results known in the literature in historical demography. In particular, we exploit the dates of birth and death to examine the mortality of individuals in the database. We also exploit the richness of the spatial characteristics contained in the family trees to analyze the internal migrations in France.