Certainty effect

As a safety effect ( engl. certainty effect) is called a cognitive bias that people value in a decision under uncertainty the difference between two probabilities then much higher if this absolute certainty can be achieved. Thus, a transition from 99 to 100 per cent is rated as more important than a 50 to 51 percent. While this is only a quantitative improvement, provides that represents a qualitative transition

Similarly, a transition from 0 to 1 percent is rated much higher than a 50 to 51 percent. This is referred to as a possibility effect (English Possibility effect). Example: To reduce the risk of disaster ( nuclear accident, amputation or similar) from 5 to 0 percent ( ie completely ruled out ), people would do much more than for the reduction from 10 to 5 percent.

Both effects show that people unlikely events irrational attach much weight. This realization is one of the improvements of the Prospect Theory over the classical expected utility theory.

Source

Daniel Kahneman (2011): Thinking, fast and slow, Allen Lane paperback, ISBN 978-1-846-14606-0, in Chapter 29, "The fourfold pattern", pp. 310-321

Certainty effect

Source

See also