Objective: To estimate the effectiveness of booster seats and of seatbelts in reducing the risk of child death during traffic collisions and to examine possible effect modification by various collision and vehicle characteristics.
Methods: A matched cohort study was conducted using data from the Fatality Analysis Reporting System. Death risk ratios were estimated with conditional Poisson regression, bootstrapped coefficient standard errors, and multiply imputed missing values using chained equations.
Results: Estimated death risk ratios for booster seats used with seatbelts were 0.33 (95% CI 0.28 to 0.40) for children age 4–5 years and 0.45 (0.31 to 0.63) for children aged 6–8 years (Wald test of homogeneity p,0.005). The estimated risk ratios for seatbelt used alone were similar for the two age groups, 0.37 (0.32 to 0.43) and 0.39 (0.34 to 0.44) for ages 4–5 and 6–8, respectively (Wald p = 0.61). Estimated booster seat effectiveness was significantly greater for inbound seating positions (Wald p = 0.05) and during rollovers collisions (Wald p = 0.01). Significant variability in risk ratio estimates was not observed across levels of calendar year, vehicle model year, vehicle type, or land use.
Conclusions: Seatbelts, used with or without booster seats, are highly effective in preventing death among motor vehicle occupants aged 4–8 years. Booster seats do not appear to improve the performance of seatbelts with respect to preventing death (risk ratio 0.92, 95% CI 0.79 to 1.08, comparing seatbelts with boosters to seatbelts alone), but because several studies have found that booster seats reduce non-fatal injury severity, clinicians and injury prevention specialists should continue to recommend the use of boosters to parents of young children.