A propensity score approach to estimating child restraint effectiveness in preventing mortality.

Confounding between the child's restraint use and driver behavior can bias restraint effectiveness estimates away from the null if survivable crashes are more common in certain restraint types. Analyzing only fatal crashes may introduce selection bias toward the null because any protective effects of a restraint type will underrepresent children in that restraint. A marginal-structural-model-type estimator suggests a 17% reduction in fatality risk for children aged 2 through 6 in child restraint systems relative to seat belts. This reduction is estimated at 22% when severe misuse of the restraint is excluded.