# **1. Introduction**

The age of first union (marriage or cohabitation) and the age of first parenting are of considerable concern both in academic and in policy communities. Indeed, these are two of the major indicators of transitions from adolescence to adulthood emphasized, for example, in the recently-published NRC/IOM panel report on transitions to adulthood in developing counties (e.g., NRC/IOM 2005). Both the age of first union and the age of first parenting are of substantial interest not only because of their implications for individual welfare and well-being over the life cycle, but also because they are strongly associated with fertility patterns that are thought to have important implications for the broader society because of externalities (at least given subsidized prices for social services such as schooling and health) as well as for the adolescents and young adults involved.

One major concern in the literature has been that cohabiting and parenting when too young (say, before age 18) limits too much the options of adolescents, particularly women, over their subsequent life cycles and further limits too much the options of their children. While there has been a general tendency for reductions in the proportions of those who are in unions at young ages in most of the developing world, substantial proportions of women still cohabit and begin parenting before they are 18. For this reason there has been substantial interest in the possibilities of delaying forming such unions and initiating parenthood. In a related vein, there is a large literature that presents positive _associations_ between schooling and age of first union and age of first parenting in many societies. Because of these associations, many have been tempted to conclude that one important reason for increasing schooling is to reduce the prevalence of entering into unions and parenthood when young.

But the many positive _associations_ between schooling attainment and ages of first union and first parenting do _not_ mean that increasing schooling would _cause_ increases in ages of first union and first parenting. There are at least three major problems in making such an inference from the available studies.

_First_ , within a dynamic life-cycle framework, schooling, union-formation and initial parenting all reflect behavioural choices that depend on observed and unobserved individual and family background and other characteristics. Some individuals and some families may have unobserved characteristics, such as ability and motivation for schooling that are rewarded in labor markets, that lead to greater investments in schooling and greater delays in union formation and first parenting. If the estimation methods used do not control for the behavioural determinants of schooling, the estimated associations between schooling and the ages of first union and first parenting may be due importantly to the impact of such unobserved factors on all of these behavioural outcomes.

_Second_ , schooling is likely to be only one important factor in union-formation and initial parenting decisions. Other aspects of individuals’ human capital (e.g., health, physical attractiveness) and of their parents (e.g., socioeconomic status) are likely to be important determinants of these decisions. Because other dimensions than schooling of individuals’ human capital are likely to be determined in part by family background and the other factors that determine schooling, if only schooling is considered as a determinant of ages of first union and first parenting, even if schooling is treated as behaviourally determined, the effect of schooling is likely to be mis-represented (probably overestimated) because in such estimates schooling partially proxies for other human capital and for family background.

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