For everyone that has three kids, you know how hard  it can be to put those three kids in a car with approved child safety car seats. It can be a challenge in many models of vehicles. But now work by Jordan Nickerson and David Solomon, professors of finance at the Massachusetts Institute of Technology and Boston College has linked the declining birth rate of American women on the design and carrying capacity of  American vehicles.

In fifty years the birth rate of American women has fallen from 2.12 children on average to 1.73. Of course the fact that there’s available birth control and  better educational and work  opportunities have impacted these statistics. But these researchers point out that declining birth rate curves do not dovetail with just those factors.

The Economist Science and Technology page describes the researchers’ study, “Car Seats as Contraception”.

The paper is available for download here.

The researchers looked at the impact of car seat policies on American birth rates for 43 years to 2017. In 1973 only small infants had to be legally in baby car seats. Legislation then evolved to make it mandatory for children to be in car seats until they are eight years old.

So could that be the reason that there are fewer three child families?

The researchers found that that there were “no detectable effects on the rates of births of first and second children, but was accompanied by a drop, on average, of 0.73 percentage points in the number of women giving birth to a third while the first two were young enough to need safety seats. That may not sound much, but it is a significant fraction of the 9.36% of women in the sample who did become third-time mothers.”

This reduced third child rearing was found in households with vehicle  access, and also was more pronounce in households with two parents.  In terms of numbers, they estimated that the reduction in births meant 8,000 less in a year, with 145,000 less births since 1980.  Ninety percent of the decline happened after 2000.

Before child safety seats it was feasible to get three young kids in the back of a sedan. But now many smaller vehicles will only fit two safety seats for children.

As the Economist observes “So, the older a child must be before no safety seat is required, the longer a family must wait before a third child will fit in the car. Sometimes, that wait will mean no third child is ever conceived and born.”

Here’s a short YouTube video on the history of the child safety car seat.

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