Big Families vs. Small Families: A Matter of Quantity vs. Quality?

At the time of the photo, the Bates family of Lake City, Tennessee, had 18 kids. They now have 19. James Ambler / Barcroft USA / Getty Images

Children in big families get less than those in smaller families. It's just math, right?

Less time with the folks than the oldest had when he or she was the only one around. Maybe fewer toys or books or games or new clothes. Altogether, with other kids in the family, there's just a little less space all around.


For years, scientists have delved into whether that truth has resulted in kids who are worse off. Some have said no. Some have tried to show that it's true.

Now, new research finds that kids from bigger families end up not as smart, with more behavioral problems as children and more problems as adults. The study concludes with a line that's like a smack in the back of the head from an older brother:

"On average, children in larger families have lowered parental investment and worse cognitive and non-cognitive outcomes."


The paper is authored by three economists; Yona Rubinstein from the London School of Economics, and Chinhui Juhn and C. Andrew Zuppann of the University of Houston.

Sharing clothes, books, toys and rooms all have an effect on kids. But, as most children from big families will tell you — and this study backs them up — the biggest effect of all those kids comes in the form of less attention from mom and dad.

"I think a lot of people may think, a new child comes, it's rough, especially in that first year or two. You're sort of adjusting, there's a new baby, you're not sleeping and all these sorts of things," Zuppann says from Houston. "But we actually find that these effects are very persistent over time. It lasts for a long time, in terms of the negative effects on the older children."

Figuring Out the Effects of Family Size

The study — "The Quantity-Quality Trade-off and the Formation of Cognitive and Non-cognitive Skills" — draws on data from the National Longitudinal Survey of Youth 1979, a U.S. Bureau of Labor Statistics database that originally surveyed more than 12,000 young men and women between the ages of 14 and 22 first in 1979, with annual interviews through 1994 and biennial ones after that.

The authors measured how much time parents spent with kids through questions on the NLSY79's HOME section (HOME stands for home observation measurement of the environment). The researchers didn't get exact numbers. But the survey's questions — like "How often do you read stories to child?", and "How often does child eat a meal with both mother and father?", and "How many times in the past week have you shown child physical affection?" — helped to form answers on who got more: single kids or kids with siblings.

And the research found that, with dwindling parental involvement as families got larger, the kids of larger families end up with lower education and earnings, more criminal behavior and a higher rate of teenage pregnancy.

The effects of larger families on kids grow especially poignant with mothers who scored low on a test that measures cognitive skills — the Armed Forces Qualification Test (AFQT) — that was administered with the NLSY79.

"When we compare households where the mother has high scores vs. the mothers who have low scores," Zuppann says, "we find that the trade-offs are really concentrated — the negative effects are really concentrated — in the households with ... the mothers with sort of lesser cognitive abilities."

The authors can't say exactly why those children suffer, but Zuppann says it may have less to do with the mother's cognitive abilities than sociological matters. "We have some suggestive evidence that those households are less able to change their working conditions. The women with high abilities ... are more likely to draw down their hours and work less, and less likely to participate in the labor force after the birth of the second child," Zuppann says. "That's less true for the mothers with low AFQT scores."

Which brings us back to a major theme in the research: The time parents spend with their kids, or the lack of it, is critical to their development and impacts their success as an adult.

Solutions That Don't Affect Family Size

Maybe one of the biggest questions that the study brings up is whether a trade-off between how many kids you have and the so-called "quality" of those kids — quantity versus quality — is necessary, or if it's something that can somehow be avoided.

"One very possible answer is that ... governmental policies could play a really important role in the development of children. Things like parental leave, or maternal leave, or child-care subsidies," Zuppann says. "I don't have an answer for what those policies should exactly look like. But this is one thing to think about, that maybe we can design policies that allow parents to have the number of children they want to have while not necessarily having detrimental effects on the other children in the household. That's the sort of large social questions that our research is driving toward."

The study has its limitations, as all do, including one fairly obvious one. It does not measure happiness in the family.

"It may be very possible that parents are happier when the second child arrives, and the trade-off is just the first child is a little bit worse off, but the parents are waay happier," Zuppann says.