Large families often capture the public's attention, from "The Brady Bunch" to "19 Kids and Counting." But new research from economists at the University of Houston offers strong evidence that children in larger families are more likely to fall behind in cognitive achievement and have behavioral and other problems.
The findings were published by the National Bureau of Economic Research. The authors include Chinhui Juhn, Henry Graham Professor of Economics at UH, Yona Rubinstein of the London School of Economics and C. Andrew Zuppann, assistant professor of economics at UH.
"Families face a substantial quantity-quality trade-off: increases in family size decrease parental investment, decrease childhood performance on cognitive tests and measures of social behavior," they wrote. "Importantly, we find that these negative effects are not merely temporary disruptions following a birth but in fact persist throughout childhood."
That persistence into early adulthood is consistent with other research pointing to the importance of early childhood experiences.
"A lot of what happens in early childhood has lasting impacts," Juhn said. "In many respects, this matters more than a lot of things that happen later in (a child's) life."
Most previous research in the field is based on data collected after children reach adulthood; this study used a dataset that tracked outcomes throughout childhood and compared outcomes of older children before and after a younger sibling was born. They found that additional children reduce "parental investment," a category defined as including time spent with children, affection, the safety of the home environment and resources – money, books and other material goods.
But the findings weren't monolithic. Children in families where mothers had above median scores on the Armed Force Qualification Test (AFQT) were less affected. Juhn said the AFQT is a proxy for socioeconomic factors. Mothers with low test scores are more likely to be poor, while those with high scores are more likely to be better educated and wealthier.
The data didn't include information about fathers, although Juhn said women with low AFQT scores are less likely to be married.
The work expands upon older research and offers explanations for some discrepancies in earlier studies. One key inconsistency: While several earlier studies found a negative relationship between family size and children's educational and labor market outcomes, a 2005 study using data from Norway found no trade-off.
Social supports and public policies in Norway may lessen the impact of increased family size, the researchers say.
"Parental investments may matter more in the U.S. where a substantial fraction of young men and women, particularly from lower income backgrounds, are at risk of not finishing high school," they wrote.
"If you are in a well-resourced family, some of these things don't apply," Juhn said. "When the second child comes along, there is less time and attention. But in an environment with more resources, it's not as binding."