In families where funds are extremely tight, siblings might report fighting for seconds at the dinner table or for access to opportunities such as music lessons or help with school expenses. A recent study in The Economic Journal bears this out. Researchers found that, in developing countries, parents with limited resources and multiple children don’t allocate those resources equally within the home. They consistently favor some of their kids over others. What’s more, the favorite children tend to be those siblings born during high-income periods, the study showed, when the family has the most access to vaccines and medical care.

As the household economic situation worsens, parents favor kids born during good times (who tend to be the strongest and healthiest) over siblings born during economic shocks. “Hence,” says coauthor Nicolas Berman, a senior researcher at Aix-Marseille University in France, “it appears that variations in income tend to reinforce initial disparities and to increase inequalities within families.”

Numerous prior papers in economics had already shown that children born during hard times have worse lifetime outcomes across the board—in health, education, and opportunity. For this study, the coauthors wanted to know whether inequalities within households contribute to those worse outcomes. According to the results, they do, with parental behavior playing a reinforcing role.

To conduct the study, the authors collected demographic health surveys from 54 developing countries, including information about individual families, such as the number of children, their ages, heights, weights, and ages at vaccination. Local authorities and organizations had conducted the surveys in multiple waves from 1986 to 2016; they included about a million children. The authors also assessed regional crops and trends in the price of those crops on the global market as a proxy for economic upswings or downturns in the area where authorities conducted each survey. Then, they made an empirical regression model to test for any effect of crop price indexes during pregnancy on the height and weight of each child during their first five years of life.

They found that negative income shocks in utero and at birth had a significant negative effect on the height, weight, and vaccine status of children at several years old. Children gestated and born during better economic times showed positive effects on health indices, and these effects persisted even when new siblings were born and income declined.

The findings “are both compelling and interesting,” says Anna Aizer, a professor of economics at Brown University in Providence, Rhode Island, who was not involved in this work. The paper’s main contribution, she says, is showing that children gestated during good times (and likely born healthier) garner more parental investment than children gestated during harder times (and likely born less healthy). Crucially, good economic times while one baby was in utero led to worse outcomes for future siblings. Other economists have asked similar questions before, she says, but with smaller datasets.

There have been two general models for how parents may behave: either they reinforce positive economic shocks by favoring healthier siblings, or they may try to compensate for negative shocks by devoting more resources to the weaker siblings. “This paper shows that in developing countries, the former seems to be most relevant,” Aizer says. “I think in higher-income settings, however, the opposite is more likely to be true.” She points to studies suggesting that better educated mothers are more likely to compensate for early life challenges, while less educated mothers are more likely to reinforce inequalities, such as birth-weight differences among children. Compensating seems to be more relevant for higher income families but reinforcing for families with fewer resources, she notes. Berman generally agrees, noting that dynamics in developed countires diverge “in multiples dimensions that potentially could lead to the reverse result to be observed.”

Looking ahead, papers like this can help inform on-the-ground interventions, the coauthors note. For example, a local government might want policies that reduce inequality in the long-term. Would an antipoverty program that writes parents a check during income swings be a good way to meet that goal? Or should policies and programs aiming for more social fairness actually target the city, village, provincial, or regional level? One next step, the coauthors note, would be to investigate how existing anti-poverty policies play out within real families, for instance, to see if those policies benefit some siblings more than others.

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