Freakonomists Dubner and Levitt look at car seats in The Seat-Belt Solution:
They certainly have the hallmarks of an effective piece of safety equipment: big and bulky, federally regulated, hard to install and expensive. (You can easily spend $200 on a car seat.) And NHTSA data seem to show that car seats are indeed a remarkable lifesaver. Although motor-vehicle crashes are still the top killer among children from 2 to 14, fatality rates have fallen steadily in recent decades — a drop that coincides with the rise of car-seat use. Perhaps the single most compelling statistic about car seats in the NHTSA manual was this one: ”They are 54 percent effective in reducing deaths for children ages 1 to 4 in passenger cars.”But 54 percent effective compared with what? The answer, it turns out, is this: Compared with a child’s riding completely unrestrained. There is another mode of restraint, meanwhile, that doesn’t cost $200 or require a four-day course to master: seat belts.
For children younger than roughly 24 months, seat belts plainly won’t do. For them, a car seat represents the best practical way to ride securely, and it is certainly an improvement over the days of riding shotgun on mom’s lap. But what about older children? Is it possible that seat belts might afford them the same protection as car seats?
The answer can be found in a trove of government data called the Fatality Analysis Reporting System (FARS), which compiles police reports on all fatal crashes in the U.S. since 1975. These data include every imaginable variable in a crash, including whether the occupants were restrained and how.
Even a quick look at the FARS data reveals a striking result: among children 2 and older, the death rate is no lower for those traveling in any kind of car seat than for those wearing seat belts.