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Peltzman Effect
Peltzman Effect
Peltzman Effect
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Overview

This phenomenon can explain why football players wearing helmets can be more prone to neck injuries; why pedestrians are at greater risk when ...

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Actionable Takeaways
  • Expect less immediate positive impacts for new safety measures. 

Understanding ...

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Limitations

Peltzman’s work was critiqued in a paper two years after its publication. Leon Robertson’s paper entitled A Critical Analysis of Peltzman’s ‘The Effects of Automobile Safety Regulation broke down a number of statistical problems with Peltzman’s work, explaining that: “The variables used in Peltzman's analysis were reviewed. It was concluded that some of them were arbitrarily chosen, that some were correlated, and that important factors were omitted. This may cause spurious and biased correlations. Peltzman's time series regression equations were reconstructed and found unstable, which makes them useless for predictions which are one basis for Peltzman's conclusions.” For those of you unfamiliar with academic discourse, them’s fighting words!

That said, the principle behind Peltzman’s work has persisted and evidence seems to demonstrate the effect does occur but generally does not negate all benefits of safety initiatives. A 2006 Dutch paper conducted an empirical study of motor vehicle safety and found that behaviour change related to the Peltzman Effect reduced less than 50% of the overall benefits. 

In Practice

Seat belts. 

This 1994 study of seat belt wearing explored behavioural adaptation by those starting to use seat belts and found that “beginning wearers (group iii) showed signs of continuing behavioral adaptation, in the form of increased speed and increased propensity for close following.”

Bike helmets. 

Cycling UK has argued against the compulsory use of helmets, explaining: “Cycle helmets have in any case not been shown to be an effective way to reduce cyclists’ injury risks. Indeed they might even be counter-productive, by encouraging drivers or cyclists to behave less cautiously, and/or by increasing the risks of neck and other injuries. By deterring people from cycling, they may also reduce the benefits that cyclists gain from ‘safety in numbers’.”

Booths Rule #2. 

Skydiving has become consistently safer over the last few decades thanks to a number of safety initiatives, some of them developed by skydiving enthusiast and inventor Bill Booth. However, Booth’s Rule #2 states, "the safer skydiving gear becomes, the more chances skydivers will take, in order to keep the fatality rate constant." Indeed, without the popularity of complex low to ground maneuvers and high speed canopies that allow for faster speeds, some claim that fatalities would be a fraction of what they were a few decades ago.

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Origins & Resources

Sam Peltzman, an economist at the University of Chicago, first described this effect in 1975 in relation to the car safety entitled The Effects of Automobile Safety Regulation. In the study, he argued that the increase of safety regulations was offset by people’s behaviour creating no change in highway deaths. The results of his report have been criticised (see Limitations above), though the effect named after the work persists. 

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