Expected utility theory (EUT), formalized by von Neumann and Morgenstern (1944), is the standard normative model of rational choice under risk. It prescribes that a rational decision maker should choose the option that maximizes expected utility — the sum of each outcome's utility (subjective value) weighted by its probability. The theory is derived from axioms (completeness, transitivity, independence, continuity) that define rational preferences.
Key Structures
- Ventromedial prefrontal cortex — A prefrontal region involved in value-based decision making, emotion regulation, and the representation of reward outcomes.
- Orbitofrontal cortex — The ventral prefrontal region critical for representing reward value, evaluating outcomes, and guiding adaptive decision making.
- Parietal cortex — The cortical region between frontal and occipital lobes, integrating sensory information for spatial representation and attention.
- Decision Making — The cognitive processes involved in selecting a course of action from among multiple alternatives, integrating information about options, outcomes, and preferences.
- Prospect Theory — Kahneman and Tversky's descriptive theory of decision making under risk, proposing that people evaluate outcomes relative to a reference point and are loss averse.
- Heuristics — Mental shortcuts or rules of thumb that simplify complex judgments and decisions, enabling fast and often adequate solutions at the cost of systematic errors and biases.
Key Functions
Prescribe that rational decision makers should choose the option with the highest expected utility (probability × subjective value), serving as the normative standard for decision theory.
The Theory
EUT improves on expected value theory by replacing objective monetary values with subjective utilities, accommodating risk aversion through a concave utility function (diminishing marginal utility of wealth). A risk-averse agent prefers a sure $50 to a 50-50 gamble for $100 because the utility of the first $50 exceeds the additional utility of the second $50. EUT has been the foundation of economic theory, financial modeling, and game theory for decades.
Violations and Alternatives
Systematic violations of EUT have been extensively documented. The Allais paradox (1953) showed that people's choices violate the independence axiom. The Ellsberg paradox (1961) showed aversion to ambiguity (unknown probabilities) beyond what EUT can explain. Preference reversals demonstrate intransitive choices. These violations motivated alternative theories: prospect theory, rank-dependent utility theory, regret theory, and support theory, each relaxing different axioms of EUT while maintaining a formal decision-theoretic framework.
Despite its descriptive failures, EUT remains the benchmark for rational decision making. Departures from EUT are defined as biases or irrationalities precisely because EUT provides the normative standard. Whether this is appropriate — whether EUT truly captures what it means to be rational given human cognitive constraints — is debated between the heuristics-and-biases tradition (which treats EUT violations as errors) and the ecological rationality tradition (which argues that EUT is not the right standard for bounded agents in uncertain environments).
Disorders
- Systematic violations in gambling disorder
- Impaired utility computation in orbitofrontal damage