Nber Working Paper Series Evidence That Seat Belts Are as Effective as Child Safety Seats in Preventing Death for Children Aged Two and Up

Over the last thirty years, the use of child safety seats in motor vehicles has increased dramatically, fueled by well publicized information campaigns and legal mandates. In spite of this movement, there is relatively little empirical evidence regarding the efficacy of child safety seats relative to the much cheaper alternative of traditional seat belts. Using data from the Fatality Analysis Reporting System (FARS) on all fatal crashes in the United States from 1975-2003, I find that child safety seats, in actual practice, are no better than seat belts at reducing fatalities among children aged 2-6. This result is robust to a wide range of sensitivity analyses, including controlling for sample selection that arises because the FARS data set includes only crashes in which at least one fatality occurs. Steven D. Levitt Department of Economics University of Chicago 1126 E 59 Street Chicago, IL 60637 and NBER [email protected] The National Highway Transportation Safety Administration (NHTSA) estimates that child safety seats have saved over 6,000 lives between 1975 and 2003, including over 400 in 2003 (Kahane 2004, Starnes 2005). In response to the apparent life-saving benefits of car seats, an expanding set of state and national regulations have been put into place. All 50 states currently require that children ride in approved safety seats. The required ages and weights up to which a child must use a safety seat vary by state, but have been steadily increasing over time (Insurance Institute for Highway Safety 2004). As a consequence, child safety seat usage has increased dramatically. Child safety seats have been heralded as one of the most successful safety innovations of recent decaces (Kahane 1986), with benefit-cost ratio estimates as high as thirty-two to one (Children’s Safety Network 1996). According to the 1997 Census of Manufactures, more than four million child car seats were purchased in 1997, with an estimated cost to consumers of more than $300 million. Given the widespread use of child safety seats and the substantial consumer expenditure on them, there is relatively little systematic empirical research evaluating their effectiveness, most of it done by NHTSA researchers (Kahane 1986, Partyka 1988, Hertz 1996). All of these studies find that child safety seats greatly reduce injuries relative to passengers who ride unrestrained. 2 Often overlooked in the public discussion of the safety of child passengers is the 2 Based on sled tests with crash test dummies and accounting for the mix of correctly and incorrectly used child safety seats in 1984, Kahane (1986) estimates that safety seats reduced both fatalities and hospitalizations by 46 percent relative to children riding unconstrained. Partyka (1988) and Hertz (1996) each use a “double pairs” comparison to evaluate restraint effectiveness. The ratio of driver fatalities to child passenger fatalities in which the child is restrained is compared to the ratio of driver to child passenger deaths when the child is unrestrained. This double pairs analysis does not condition on any additional variables except whether the driver is wearing a seat belt and whether the child is seated in the back seat. Partyka (1988), using data from 1982 to 1987, estimates that child safety seats are 69 percent effective in reducing fatalities of infants and 47 percent effective in reducing fatalities for children aged 1-4. Hertz (1996), using a similar methodology but later data, finds that child safety seats reduce fatalities of infants by 71 percent and 58 percent in cars and light trucks/vans respectively relative to riding unrestrained. For children aged 1-4 the corresponding numbers are 54 and 59 percent.