Probability range and probability distortion in a gambling task.

In decision making under risk, adults tend to overestimate small and underestimate large probabilities (Tversky & Kahneman, 1992). This inverse S-shaped distortion pattern is similar to that observed in a wide variety of proportion judgment tasks (see Hollands & Dyre, 2000, for review). In proportion judgment tasks, distortion patterns tend not to be fixed but rather to depend on the reference points to which the targets are compared. Here, we tested the novel hypothesis that probability distortion in decision making under risk might also be influenced by reference points—in this case, references implied by the probability range. Adult participants were assigned to either a full-range (probabilities from 0–100%), upper-range (50–100%), or lower-range (0–50%) condition, where they indicated certainty equivalents for 176 hypothetical monetary gambles (e.g., “a 50% chance of $100, otherwise $0”). Using a modified cumulative prospect theory model, we found only minimal differences in probability distortion as a function of condition, suggesting no differences in use of reference points by condition, and broadly demonstrating the robustness of distortion pattern across contexts. However, we also observed deviations from the curve across all conditions that warrant further research.