Is fertility still correlated to the number of siblings? A cross-generational study including half-siblings

Anne Solaz, Institut National d'Études Démographiques (INED)
Eva Beaujouan, Wittgenstein Centre (IIASA, VID/ÖAW, WU)

The correlation between parents’ and offspring’s fertility has received large attention in demographic and economic literature, but has rarely been studied over a long period of time. Both the boom in fertility after the Second World War and the reduction of family size since the 70’s might have affected the magnitude and the nature of this relationship. Has the relationship between parents’ and children’s fertility changed? The originality of this contribution stands in its long-term approach: we compare French generations over two third of a century (men and women born since 1925). Additionally, with the development of step-families, the siblings’ picture is extended to include half and step siblings the individual grew-up with. Finally, we ask whether men and women are affected in the same way by their family of origin. We use the recent French Enquête Famille et Logements 2011 (EFL, Ined-Insee), a section of the census oriented towards the family. This data source provides extensive information about fertility history, last partnerships, education and working background of both the respondent and his parents, and the number of full- and half-siblings for 360,000 men and women aged 18 or more. Our methodology is based on different indicators (crude and adjusted correlations, elasticities) and estimations methods (Poisson and quantile regressions) to take into account various technical problems such as the discrete and non linear nature of fertility variables, the risk of presence of confounding factors and the variability of fertility levels on the studied period. First results show that the intergenerational relationship between family sizes is weak in France, around 0.12-0.15, with a decreasing effect in most recent generations. Only numerous families are drivers of the correlation nowadays, whereas only- and one-children were also driving it sixty years ago. These results have to be detailed and confirmed using more sophisticated methods.