# Certainty effect

Main article: Prospect theory

Certainty effect refers to the psychological effect resulted from the reduction of probability from certainty to probable (Tversky & Kahneman 1986). It is an idea introduced in prospect theory.

Normally a reduction in probability of winning a reward (e.g. reduce from 80% to 20% of chance of winning a reward) creates psychological effect such as displeasure to individuals, which leads to the perception of loss from the original probability thus favoring a risk-aversion decision. However, the same reduction results in larger psychological effect when it is done from certainty than from uncertainty.

## Example

Tversky & Kahneman (1986) illustrated the certainty effect by the following examples.

First, consider this example:

Which of the following options do you prefer?

• A. a sure gain of \$30
• B. 80% chance to win \$45 and 20% chance to win nothing

In this case, 78% of participants chose option A while only 22% chose option B. This is the typical risk-aversion phenomenon in prospect theory and framing effect.

Now, consider this problem:

Which of the following options do you prefer?

• C. 25% chance to win \$30 and 75% chance to win nothing
• D. 20% chance to win \$45 and 80% chance to win nothing

In this case, 42% of participants chose option C while 58% chose option D.

Compare to the first problem, both options winning probabilities were quarter of the original (A->C:100%/4=25%, B->D:80%/4=20%) . However, individuals show a greater preference in the second option in the second problem while expected utility remained the same.