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Risk compensation

In ethology, risk compensation is an effect whereby individual people may tend to adjust their behaviour in response to perceived changes in risk. It is seen as self-evident that individuals will tend to behave in a more cautious manner if their perception of risk or danger increases. Another way of stating this is that individuals will behave less cautiously in situations where they feel "safer" or more protected.


There is evidence that suggests that such an effect is seen in humans, associated with the use of safety features such as car seat belts and bicycle helmets. The evidence is particularly compelling for the case of antilock braking systems. The existence of this balancing behaviour does not mean an intervention does not work; the effect could be less than, equal to, or even more than the true efficacy of the intervention, depending on how well the perceived efficacy matches actual efficacy - and this will differ from individual to individual. It is likely to be least when an intervention is imperceptible and greatest when an intervention is intrusive or conspicuous.

The theory grew largely out of investigations of road safety interventions. It was noted that some interventions had failed to achieve the forecast savings in lives and injuries (e.g. Adams' discussion of seatbelt legislation). Theorists speculated that while the studies demonstrated that the probability of injury given a crash had reduced, the fact that the overall probability of injury was unchanged indicated that there must have been some change in the probability of crashing.

Related research

Anti-lock brakes

There are at least three studies which show that drivers' response to antilock brakes is to drive faster, follow closer and brake later, accounting for the failure of ABS to result in any measurable improvement in road safety. The studies were performed in Canada, Denmark and Germany.

A study led by Fred Mannering, a professor of civil engineering at Purdue University supports risk compensation, terming it the "offset hypothesis".

Bicycle helmets

A study published in the March 2007 issue of Accident Analysis & Prevention stated that drivers drove an average of 8.5 cm closer, and came within 1 meter 23% more often, when a cyclist was wearing a helmet. Statements made in the report included: “The closer a driver is to the cyclist, the greater chance of a collision.”, “Drivers passed closer to the rider the further out into the road he was.”, “The bicyclist’s apparel affects the amount of clearance the overtaking motorist gives the bicyclist”.

Ski helmets

“There is no evidence they reduce fatalities,” said Dr. Jasper Shealy, a professor from Rochester Institute of Technology who has been studying skiing and snowboarding injuries for more than 30 years. “We are up to 40 percent usage but there has been no change in fatalities in a 10-year period.” There is evidence that helmeted skiers tend to go faster.

Seat belts

In 1981 John Adams published a paper, The efficacy of seatbelt legislation: A comparative study of road accident fatality statistics from 18 countries, Dept of Geography University College, London 1981 - published in 1982 by the Society of Automotive Engineers.[1] This showed that in the countries studied, which included states with and without seat belt laws, there was no correlation between the passing of seat belt legislation and the total reductions in injuries or fatalities. When all associated fatalities and injuries in road accidents were included, it appeared that some accidents were being displaced from car drivers to pedestrians and other road users.

This paper was published at a time when Britain was considering a seat belt law, so the Department of Transport commissioned a report into the issue. In the event the report's author, Isles, agreed with Adams' conclusions. The Isles Report was never published officially but a copy was leaked to the Press some years later. The law was duly passed and subsequent investigation showed some reduction in fatalities, the cause of which could not be conclusively stated, due to the simultaneous introduction of evidential breath testing.

Other research has taken groups of drivers, including those who did and did not habitually wear seat-belts, and measured the effect on driving style in the habitually unbelted. The drivers were found to drive faster and less carefully when belted.


Booth's rule #2, coined by skydiving pioneer Bill Booth, states that "The safer skydiving gear becomes, the more chances skydivers will take, in order to keep the fatality rate constant". Even though skydiving equipment has made huge leaps forward in terms of reliability in the past two decades, and safety devices such as AADs have been introduced, the fatality rate has stayed roughly constant since the early 1980s.[2] This can largely be attributed to an increase in the popularity of high performance canopies, which fly much faster than traditional parachutes. High speed manoeuvres close to the ground have increased the number of landing fatalities in recent years,[3] even though these jumpers have perfectly functioning parachutes over their heads.

Speed limits

A 1994 study by Jeremy Jackson and Roger Blackman, using a driving simulator, showed that although increased speed limits and reduced speeding fines significantly increased driving speed, there was no effect on accident frequency. It also showed that increased accident cost caused large and significant reductions in accident frequency but no change in speed choice. The abstract states that the results suggest that regulation of specific risky behaviors such as speed choice may have little influence on accident rates.

Safety equipment in children

At least two experimental studies have suggested that children who wear protective equipment are likely to take more risks.

Use of condoms in AIDS prevention

Harvard researcher Edward C. Green argued that the risk compensation phenomenon could explain the failure of condom distribution programs to reverse HIV prevalence. Dr Green says his ideas are motivated by empirical research, rather than by any moral or religious association with the Catholic Church. Green provided more detailed explanations of his views in an op-ed article for The Washington Post ("The Pope May Be Right") and an extended interview with the BBC. This view is shared by other specialists.

Risk homeostasis

An associated theory is known as risk homeostasis. This extends risk compensation theory somewhat, although in practice the two terms are often used interchangeably.

Professor Gerald J. S. Wilde illustrates this by reference to the Swedish experience when they changed from left- to right-hand drive in 1967.[4] This was followed by a marked reduction in the traffic fatality rate, but the trend returned to its previous values after about 18 months. Drivers had responded to increased perceived danger by taking more care; as they became accustomed to the new regime, the additional care evaporated.

Risk compensation is now widely accepted, but risk homeostasis, which goes much further, has a much smaller following.

See also

External links