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  • A new study finds that when the law requires both of a family’s two existing kids to be in car seats, the family becomes less likely to have a third child. Tweet This
  • Among women ages 18–35 with two kids, about 9.36% give birth each year, but having both the older kids bound by car-seat laws reduces that by about 0.73 percentage points. Tweet This

When we decided to have a third kid, my wife and I needed to have a difficult conversation about another member of the family: our light-blue 2013 Hyundai Elantra, the first car we bought together after leaving the dense misery of New York City. The older kids were two and five, and the poor vehicle just didn’t have the space for two car seats and a booster in the back. We ultimately spared it an uncertain fate in the secondhand market, but only because we already had a minivan too. Now we use the van when the baby is with us, take the car when one of us heads out alone or with one or both of the elder two, and park the Elantra on the road so there’s no conflict in our single-lane driveway.

If a new working paper from Jordan Nickerson and David H. Solomon is to be believed, this kind of vehicle Tetris is more than a mild annoyance for many American families. The study finds that when the law requires both of a family’s two existing kids to be in car seats, the family becomes less likely to have a third child. Among women ages 18–35 with two kids, about 9.36% give birth each year, but having both the older kids bound by car-seat laws reduces that by about 0.73 percentage points.

Most of the time, these parents seem to be forgoing, not just delaying, another birth. And more and more parents have faced this constraint over time: Car-seat laws only began in the 1980s, but today, the average U.S. state doesn’t let kids ride with just a seat belt until after their seventh birthday.

The study is carefully designed and worth taking seriously, though some limitations—and the sheer complexity of the undertaking—also warrant caution.

If I tell you that car-seat laws correlate with reduced fertility, your first instinct might be that the relationship is spurious. Perhaps the adoption of aggressive car-seat laws and a preference for smaller families are both driven by the same underlying cultural factors, for instance—especially the over-the-top "safetyism" that makes parenthood so labor-intensive these days. The study’s key strength is that it goes out of its way to address such concerns. It looks specifically at situations where a family has two kids and state law requires both to be in car seats, and checks to see if something is going on with such families that isn’t happening to similar families not facing this problem.

It controls for fertility trends in detail—so much detail that if women with two kids in a specific county start giving birth less often (and this pattern applies regardless of whether the kids are young enough to need car seats), that will be accounted for. It also takes account of the demographics of each mother, as well as the precise ages of the older children, such that its “comparisons are between, for instance, families with a six-year-old and a four-year-old, where in some [states and years] both are required to be in car seats, and in others they are not.” The authors further check to see if they find fertility-dampening effects on families that don’t own cars or have only one child bound by a car-seat law, which would suggest something is wrong with their approach, but they don’t find such effects.

This study could be wrong—any study could. But the rigorous design means it can’t simply be waved away.

The paper then explores how different demographics are affected by car-seat laws, reaching results that are interesting and sometimes a bit puzzling. For instance, the effect seems stronger among those with higher incomes, which is counterintuitive because poorer people are less likely to be able to afford new vehicles. The authors suggest that “large cars like minivans also have certain class and aesthetic connotations that may make people reluctant to switch, even when they can afford to,” and that richer families might be more likely to comply with the law. I would add that wealthier parents tend to plan their births much more aggressively,1 meaning they could be more likely to get anxious about things like where to put the stupid car seats.

The authors find a weirder effect on single moms (or, technically, households with no adult male present). It would be easy to explain a result where single moms were less affected, both through the planning point I made above and because older kids in boosters can sometimes sit in the front passenger seat if it's unoccupied. But they actually find the opposite effect here: Single moms seem more likely to have a third kid when the older two have to be in car seats. That's pretty bizarre and makes one wonder if there's a mistake somewhere.

There are some other limitations worth noting as well. For example, the study relies on census surveys going back to 1980, and it infers the birth history of each woman from the composition of her household when she was surveyed. For example, if a woman has a three-year-old and a five-year-old, it's assumed she gave birth three years ago and five years ago, but not in other years. This allows the researchers to analyze more birth decisions than they could if they only focused on births during the survey year, but it will miss kids who live elsewhere or have passed away. These errors could correlate with car-seat laws if the laws sometimes, say, push a divorced woman to let her ex-husband take custody of a kid. (Hat tip to Lyman Stone for pointing this out to me.)

It's also important to bear in mind that researchers make mistakes sometimes, even with relatively simple analyses—and this one is not simple at all. To figure out what car-seat laws were in effect in each state and year, for example, the authors had to go through the histories of car-seat statutes in all the states. And when the laws applied to kids of certain weights rather than ages, they cross-referenced the weight limits with other data to see what ages the weights typically corresponded to. Not to mention all the computer code that must have been needed to process the census data into the form they needed for their analysis.

We should wait until the paper is published and others confirm the result before taking this too seriously. But what does it imply if it's true?

To flesh out the trade-off we're making, the authors do some extra analyses calculating how many traffic fatalities car-seat laws prevent. The answer is relatively few: While these laws prevent about 8,000 births per year, they save somewhere between zero and 140 lives.2 Births and deaths prevented are not comparable in moral terms—I’d much rather decide not to have another kid than see one of my kids die3—but it does seem we are stopping a lot of births for each death we prevent. And don't forget that we’re talking about laws mandating car seats, not about whether car seats should be available to those who want them.

If this study holds up, loosening car-seat rules—and rooting out other “safetyist” regulations that make parenthood needlessly expensive—might be a good idea. It could give families more freedom and more kids with little increase in risk.

Robert VerBruggen is an Institute for Family Studies research fellow and a policy writer for National Review Online.

*Photo credit: Unsplash

1. See, for instance, Isabel Sawhill’s discussion of “drifters” vs. “planners” in Generation Unbound.

2.The authors’ best estimate is 57. In 2017, there were 654 total car-crash deaths for children eight and under, so this is roughly an 8 percent decrease.

3. The less said about the authors’ discussion of this distinction, the better. “People’s acceptable price to acquire a good they don’t yet own is generally lower than their price to part with a good already in their possession, a phenomenon known as the endowment effect . . .”