Divorce and Diapers

Anxious about the long-term effects of depressed fertility, demographers are pondering unexpected questions these days. One of these questions—might divorce actually foster fertility?—recently received attention from a team of demographers from Sweden, Canada, and Austria, countries that all share the dubious characteristic of sub-replacement fertility, with Austria reporting the lowest fertility.

Acutely aware that “during the last century, virtually every wealthy society experienced long-term declines in fertility,” the researchers certainly recognize that divorce can depress fertility. After all, when a couple divorces, that virtually guarantees that they will have no more children together. On the other hand, when a divorced woman remarries, she and her new husband will often choose to have a child to affirm their identity as a (re)married couple. “The value of a shared child is unique,” the researchers remark, “signaling the couple’s status as a family and their commitment to each other.”

The researchers thus see divorce both depressing and stimulating fertility. “Declines in union formation and union stability,” they write, “have made it more difficult for individuals to attain their desired number of children in a single union while increasing the probability of additional children in a new union. The balance between these two opposing effects may make the difference between above- or below-replacement fertility.”

To determine whether divorce does more to depress or to stimulate fertility, the researchers use data for French women born in the 1930s through the 1970s to develop microsimulation models “to generate hypothetical populations of women with different union and childbearing histories.” These models do, in fact, confirm the reality of a “stepfamily effect” on fertility. In other words, “women whose children were born in a single union have lower birth rates than women who have had children with a previous (resident or nonresident) partner.” The researchers conclude that “because first-time parents are highly likely to have two children together,” the stepfamily effect is “particularly significant for third and fourth births.”

Still, the researchers acknowledge evidence indicating that the fertility enhancement fostered by the “stepfamily effect” is “somewhat moderated by lower rates of repartnering for women with children from their first union and by higher rates of dissolution for stepfamily unions compared with unions with only shared children.” In other words, “the additional children some stepfamilies might produce is offset by higher rates of dissolution and reduced time in the union.”

The impact upon fertility of union (in)stability indeed looms large when the researchers weigh the stepfamily effect against the broader effect on fertility of marital failure. Women who see their first marriage fail do not always remarry or may do so only after a relatively long period of singleness. And singleness, even in progressive, broad-minded France, means low fertility. “First-birth rates,” the researchers explain, “are five times as high and second-birth rates are twice as high in coresident unions than during periods of singlehood.” Inevitably, that means that “the longer women spend out of union during their childbearing years, the lower their expected number of children.” Stressing that women’s singleness “makes more difference for first and second births, when such births constitute the vast majority of all births, means that [women’s] periods out of union remain important for replacement-level fertility.”

Consequently, even though the stepfamily effect does help push fertility higher, the researchers’ mathematical model is a strong warning to any policymakers foolish enough to promote marital instability in the hopes of so recovering replacement-level fertility for their country. The researchers conclude that, overall, “a population with stable unions would produce more children than one in which all unions dissolved, between one-third and one-half of a child per woman.”

Conscious of clear evidence that “children also benefit from stable partnerships,” the researchers can, in fact, endorse a social regime fostering stable marriages as more than just a demographic strategy for keeping a nation’s numbers from dwindling. Unfortunately, however, so long as marriage rates remain low and divorce rates remain high, obstetricians in more than a few countries are going to find they have less work than the morticians.

(Elizabeth Thomson et al., “Union Instability as an Engine of Fertility? A Microsimulation Model for France,” Demography 49.1 [2012]: 175–195.)