Daniel Kahneman was an Israeli-American psychologist whose collaboration with Amos Tversky produced some of the most influential work in twentieth-century social science. Their prospect theory provided the first mathematically rigorous alternative to expected utility theory, and their heuristics-and-biases program revealed systematic departures from rational judgment that reshaped economics, public policy, and medicine.
Prospect Theory
v(x) = x^alpha for x >= 0 (alpha ~ 0.88)
v(x) = -lambda*(-x)^beta for x < 0 (lambda ~ 2.25)
pi(p) = probability weighting function
Prospect theory introduced three departures from expected utility theory. Reference dependence: outcomes are evaluated as gains or losses from a reference point. Loss aversion: losses loom approximately twice as large as equivalent gains. Diminishing sensitivity: marginal impact decreases with distance from the reference point. Combined with probability weighting, these features explain the Allais paradox, the endowment effect, and simultaneous purchase of insurance and lottery tickets.
Kahneman's Nobel was awarded for integrating insights from psychological research into economic science. His lecture emphasized the work was fundamentally a collaboration with Tversky, who died in 1996 and would have shared the prize.
Heuristics, Biases, and Dual-Process Theory
Kahneman and Tversky demonstrated that people rely on cognitive shortcuts -- representativeness, availability, anchoring -- producing systematic deviations from normative standards. This laid groundwork for Kahneman's dual-process theory in Thinking, Fast and Slow (2011), distinguishing System 1 (fast, automatic) from System 2 (slow, deliberate) processing.
Legacy and Impact
Cumulative Prospect Theory (Tversky & Kahneman, 1992) resolved technical limitations of the original formulation. Loss aversion, framing effects, and probability weighting have become standard tools in behavioral economics, finance, public policy, and medical decision making.