Working Paper: NBER ID: w7210
Authors: Steven D. Levitt; Jack Porter
Abstract: Measurement of seat belt and air bag effectiveness is complicated by the fact that systematic data are collected only for crashes in which a fatality occurs. These data suffer from sample selection since seat belt and air bag usage influences survival rates which in turn determine whether a crash is included in the sample. Past researchers either ignored sample selection or adopted indirect estimation methods subject to other important biases. We propose a simple, but novel, solution to the selection problem: limiting the sample to crashes in which someone in a different vehicle dies. Under relatively weak conditions, consistent estimates can be obtained from this restricted sample. Empirically, we find seat belts to be more effective in saving lives than most previous estimates. Air bags, however, appear to be less effective than generally thought. If our coefficients can be generalized to all crashes, the cost per life saved with seat belts is approximately $30,000, compared to $1.6 million for air bags.
Keywords: No keywords provided
JEL Codes: C20; R40
Edges that are evidenced by causal inference methods are in orange, and the rest are in light blue.
| Cause | Effect |
|---|---|
| Seat belt usage (R48) | Reduced risk of death in crashes (R48) |
| Air bags (L62) | Reduced death rates in direct frontal crashes (J17) |
| Air bags (L62) | Reduced fatalities in crashes (averaged over all types of crash impacts) (R48) |
| Sample selection issue (C34) | Overestimated effectiveness of air bags (J17) |