Car Seats as Contraception

Jordan Nickerson and David Solomon, “Car Seats as Contraception,” Social Science Research Network, September 22, 2020, https://papers.ssrn.com/sol3/papers.cfm

Bottomline, “…First, when conditioning on women that give birth to a second child, we examine the lifetime probability of having a third child. Each additional year that the two eldest children are required to be in car seats results in a 0.60 percentage point reduction in the lifetime probability of having a third child. Second, we embed our panel data estimations into dynamic simulations which incorporate potential offsetting effects. We estimate 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. When comparing simulated birth decreases with predicted changes in births from our base regressions (which only measure contemporaneous effects), we estimate that approximately 71% of the contemporaneous effect is permanent….”

Here they explain their mechanism, “…These laws can significantly raise the cost of having children for women who already have two young children, and are considering a third. While the particular type of mandated restraining device varies, many cars cannot easily accommodate three child seats in the back row of seats, as would be needed if both front seats are occupied by adults. This especially increases the cost of a third child for many families, by necessitating the purchase of a larger car. The most practical options, like minivans, have additional problems of being expensive and unfashionable. We exploit the specific nature of costs associated with a third child, along with considerable variation in mandated ages over states and years, to identify the impact of state car seat laws on fertility. Using census data on the number and age of children for each woman surveyed,we estimate the effect of these laws on birthrates from 1973 to 2017. 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. 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…”

But as the same time the associated costs of having to buy a bigger car has lowered fertility“…Using census data and state-year variation in laws,we estimate that when women have two children of ages requiring mandated car seats, they have a lower annual probability of giving birth by 0.73 percentage points. Consistent with a causal channel, this effect is limited to third child births, is concentrated in households with access to a car, and is larger when a male is present (when both front seats are likely to be occupied)…. . 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% of this decline being since 2000….”

Unintended consequences, car seat laws. They did limit child deaths, paper estimates, “…these laws prevented…57 car crash fatalities of children nationwide in 2017…”but their cumulative impact was likely limited, “…To give context, it is worth noting how many children’s car crash fatalities there are in the first place in the U.S. In 1978, the number of fatalities for children age 0-8 was 2,392. By 2017, this had declined 73% to 654 total. However, this is almost exactly the same as the 72% decline in fatalities for children ages 9-12 over the same period from 975 to 273 (who were largely unaffected by these laws). In other words, back of the envelope approximations are consistent with the small numbers we document….”