Since the 1970s, child safety seats have been made mandatory in most western countries. And since then, the age at which children are allowed to 'graduate' from a safety seat to wearing a seat belt without the safety seat has only increased. That creates a problem if you have a large family, because mid-sized and smaller cars are simply not large enough to fit more than two safety seats in the back. That places an additional cost on families that want to grow beyond two children, since they would need a larger vehicle such as a people-mover or minivan. That significantly increases the cost of having a third small child, so a reasonable question is, have these child safety seat laws affected fertility rates?
That is the question that this new working paper by Jordan Nickerson (MIT) and David Solomon (Boston College) seeks to answer. They use data from the U.S. Census (1990 and 2000) and the American Community Survey (2000-2017), and construct a retrospective panel of women aged 18-35 based on their age and the ages of their children at the time of the survey. That results in nearly 70 million female-year observations. Using that dataset, they then look at the effect of child safety seat laws on the probability of a woman having a third child, when they already have two children that would need child safety seats. They 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. This represents a large decline, as the probability of giving birth for a woman age 18-35 with two children already is 9.36% in our sample.
Of course, this is correlation rather than causation, but Nickerson and Solomon then try to exclude other explanations, showing that:
...we do not find significant effects of car seat laws at other birth margins where car-seat-related crowding is unlikely to be an issue. For instance, there are no significant differences in birth rates when the woman has only one child total of car seat age, or two children total where only one child is required to be in a car seat.
And:
We find that the estimated effects are driven entirely by households with access to a car, consistent with car usage mattering directly. The effect is also concentrated in households where there is an adult male in the household, increasing the likelihood that both front seats are occupied by adults.
So, the results seem plausible. Fertility rates did decline as car safety seat laws expanded in scope. How many births were 'prevented' as a result? Using a simulation model based on their regressions, Nickerson and Solomon find that:
...switching from an eight-year-old mandate to a four-year-old mandate would result in the average woman having 0.0076 more children. In 2017, we estimate that car seat laws lead to a permanent reduction of approximately 8,000 births, and have prevented 145,000 births over our sample period, with 60% of this effect being since 2008. By contrast, if current laws had applied over the whole sample, we estimate there would have been a further 350,000 fewer births.
So, there may have been around 145,000 fewer children born as a result of these laws. How many lives did the car seat laws save? It appears the impact of the laws, if any, was slight, based on car crash data going back to 1975:
Using similar fixed effects specifications as our birth rate tests, we find that the estimated impact of car seat laws on deaths of children below age eight is miniscule. Our best estimates are that existing car seat mandates prevented 57 fatalities nationwide in 2017, with the most favorable estimates being 140 fatalities prevented. In the vast majority of specifications, we are unable to reject a null hypothesis of zero lives saved.
That leads to a really perverse comparison. Car seat laws may have saved thousands of children's lives, but at the same time prevented hundreds of thousands of children from being born in the first place. As Nickerson and Solomon note:
Ignoring the financial cost of purchasing safety seats, these estimates allow one to calculate the implied ratio of the value of a child’s life saved (conditional on them being born) versus the value of a child’s life prevented (children who might have been born, but were not). We estimate this ratio to be between 57 and 141.
Why would society be much more willing to save a child's life, in comparison to having a child born in the first place? Nickerson and Solomon first suggest endowment effects:
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.
In this context, once a family is endowed with a child, they would be willing to pay a lot to lower the risk to that child's life, much more than they would have been willing to pay to add a child to their previously smaller family. This arises because of loss aversion. People value losses much more than equivalent gains - in this case, the loss of a child is a much greater negative for the family than is the positive of gaining a child.
That might explain part of the effect, but I think this is more likely:
There is also a large difference in salience between the dramatic event of a small child dying in a car crash, versus the largely unseen effect of a family who wanted another child deciding that the cost is too high.
This relates to Thomas Schelling's observation about the difference between the value of an 'identified life' and the value of a 'statistical life'. Schelling noted the paradox that a community that was willing to pay hundreds of thousands of dollars to save the life of a child that fell down a mineshaft, might simultaneously be unwilling to pay tens of thousands of dollars on highway improvements that would save on average one life every year. Once a child is born, they are an 'identified life', and paying to reduce risks to their life is a valuable expense. However, before a child is born they are simply a 'statistical life', since they only exist in the future with some probability.
Nickerson and Solomon also note that:
...policymakers do not understand the magnitude of the tradeoffs involved, and either overestimate the importance of safety seats on car crash fatalities, and/or underestimate the effects on fertility.
No doubt about that. It isn't the sort of trade-off that would occur to your average policy-maker. However, as Nickerson and Solomon conclude:
The current tradeoff is particularly perverse, given the sheer magnitude by which the unintended consequences exceed the intended consequences.
[HT: Marginal Revolution]
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