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Risk homeostasis theory: an overview
  1. Gerald J S Wilde
  1. Department of Psychology, Queen's University, Kingston, Ontario K7L 3N6, Canada
  1. Correspondence to: Professor Wilde.

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There is an odd coexistence between two conflicting safety policies that may well be pursued by the same accident prevention agency. The first seeks to improve safety by alleviating the consequences of risky behaviour. It may take the form of seat belt installation and wearing, airbags, crashworthy vehicle design, or forgiving roads (collapsible lamp posts and barriers). This policy offers forgiveness for a moment of inattention or carelessness. The second policy seeks to improve safety by making the consequences of imprudent behaviour more severe and includes things such as speed bumps, narrow street passages, and fines for violations. Here, people are threatened into adopting a safe behaviour; a moment of inattention or carelessness may have a dire outcome.

While these two policies seem logically contradictory, neither is likely to reduce the injury rate, because people adapt their behaviour to changes in environmental conditions. Both theory and data indicate that safety and lifestyle dependent health is unlikely to improve unless the amount of risk people are willing to take is reduced.

Choice of denominator

In any discussion about injury prevention the criterion of success should be clearly specified, or else confusion abounds.1, 2 What is it that we want to achieve: fewer accidents per unit distance driven? Per hour of exposure to traffic? Or per head of population per year?

Sometimes the choice of denominator is obvious. We wish to reduce the number of suicides per head of population, not per pistol or km of available rope. Success in promoting electrical safety is not measured in terms of fewer cases of electrocution per kwh consumed.

In the domain of traffic, do we want to provide more mobility per case of death or injury, or do we want fewer cases of death and injury? That these two measures of success are not interchangeable is …

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