Risk Homeostasis and Peltzman Effect are two concepts relating to how humans react to risks.
Risk Homeostasis is the notion that our personal psychological frameworks comprise a target level of risk towards which we direct our efforts.
We measure risk on our own “risk thermostat.” Because the risk in our environment changes continuously, we are incessantly forced away from our target risk level, but revert toward it by counteracting those external influences.
If the perceived risk of a situation exceeds our target level, we undertake defensive actions to reduce the risk. And if the perceived risk is lower than our target level, we attempt to increase our risk back to our target level by exposing ourselves to dangerous actions.
Consequently, people take more risks when they’re forced to act more carefully. For instance, requiring motorcycle bikers to wear helmets may make them take more risks—to maintain their level of thrill, not to get into accidents.
Peltzman Effect is the notion that people respond to increased safety by adding new risks. The namesake, economist Sam Peltzman, argued in 1975 that when automobile safety rules were introduced, at least some of the benefits of the new safety rules were counterbalanced by changes in the behavior of drivers. Peltzman posited that making seatbelts mandatory for cars resulted in reducing the number of occupant fatalities, but increased pedestrian casualties and collision-related property damages.
Peltzman made a case that even though seatbelts reduced the risk of being severely injured in an accident, drivers compensated by driving aggressively and carelessly—driving closer to the car ahead of them, for instance—so as to save time or maintain their level of thrill, even at the risk of causing damage beyond themselves and their cars.
Risk Homeostasis and Peltzman Effect remain controversial theories. Despite their apparent relevance, the prevailing evidence remains inadequate and inconclusive about how people behave less cautiously when they feel more protected and vice versa.
Further, Risk Homeostasis and Peltzman Effect challenge the foundations of safety and injury-prevention policies. They assert that the only effective safety measures are those that alter individuals’ desired risk level. Anything that barely modifies the environment or regulates individuals’ behavior without affecting their target risk levels is useless.