Cohabitation, Marriage, and First Birth: The Interrelationship of Family Formation Events in Spain

In this paper, we investigate (1) the mutualcausal relationship between first unionformation and first childbirth, and (2) theexistence of constant unmeasured determinantsshared by these two events. We argue that thesedeterminants mainly consist of valueorientations that are heterogeneous in thepopulation. We apply event-history techniquesto retrospective survey data on Spain, allowingfor unobserved heterogeneity components whichsimultaneously affect the two processes. Ourfindings confirm the existence of a strongselection effect, which influences both unionformation and first birth. When controlling forthese shared factors, we find that the risk ofconception increases immediately at marriage,and it continues to be high during thefollowing four years. Entry into cohabitation,in contrast, produces a much smaller increasein the relative risk of conception. The effectof conception on union formation isparticularly strong during pregnancy, but itdeclines sharply after delivery.