Are car seat mandates responsible for reducing the number of children born each year? A provocative new study claims that the steady upward creep in the ages at which states mandate children use a car seat is prompting women to either postpone or opt against having a third child.
The paper, by Jordan Nickerson of the Massachusetts Institute of Technology and David Solomon of Boston College, argues that most vehicles cannot fit a third car seat in the back row, necessitating the purchase of a larger car if a parent is going to cart around three children at once. That added cost, they argue, disincentivizes some women from having a third child.
"We find that when a woman has two children below the car seat age, her chances of giving birth that year decline by 0.73 percentage points," write Nickerson and Solomon, relying on U.S. Census Bureau data on the age and number of children for each woman surveyed. "This represents a large decline, as the probability of giving birth for a woman age 18-35 with two children already is 9.36 [percent] in our sample."
To tease out the impact of car seat laws, the paper controls for a number of variables, including urban density, household income, and whether a male parent is present. As states increase the car seat age, the more pronounced this effect becomes, as it's more likely that three children will simultaneously be required to be in a car seat.
The nationwide average minimum age at which a child can ride in a car with just a seat belt rose from just under three years old in the mid-1980s to four years old by 2000. Today, the nationwide average is a few months under eight years old. This steady increase, the paper suggests, could help explain why fertility rates have declined in the past decade despite a long-running economic recovery that would normally encourage more childbirths.
These laws could also allow more children to live, of course, by saving their lives during car crashes, but the paper argues that the effect on birth rates is larger. The changes "prevented only 57 car crash fatalities of children nationwide in 2017," it reads. "Simultaneously, they led to a permanent reduction of approximately 8,000 births in the same year, and 145,000 fewer births since 1980, with 90 [percent] of this decline being since 2000."
Are Nickerson and Solomon right? Maybe, but there are reasons to be skeptical. It's a correlational study, and the authors have to control for a large number of variables to try to tease out the effect of car seat laws on fertility.
A post at the blog Less Wrong also questions the underlying premise of the paper, noting that parents could avoid the costs of having to purchase a larger car by buying narrower car seats, and that there are car seats on the market that would still manage to fit three abreast in even small cars.