Daniel Kahneman Nobel Lecture

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comes are embedded in a longer list (Tversky & Kahneman, 1982, 1983;

Mellers, Hertwig, & Kahneman, 2001). Tversky and Kahneman (1983) 

also found that statistically naïve respondents made conjunction errors

even in a direct comparison of the critical outcomes. As in the case of 

extension neglect, however, conjunction errors are less robust in within-

subject conditions, especially when the task involves a direct comparison

(see Kahneman & Frederick, 2002 for a discussion). 

• Hsee (1999) asked participants to price sets of dinnerware offered in a

clearance sale. One of the sets (A) consisted of 24 pieces, all in good con-

dition. The other set included the same 24 pieces, plus 16 additional

pieces, of which 7 were in a good condition and 9 were broken. When

each respondent evaluated only one set, mean willingness to pay (WTP)

was $33 for the smaller set and $23 for the larger set (p < .01). In contrast,

participants who evaluated both sets were consistently willing to pay more

for the larger set. List (2002) observed similar violations of dominance

with a different good (sets of baseball cards), in a real market situation.

• Problems of the following kind have been used in several experiments

(Kahneman & Tversky, 1972; Griffin & Tversky, 1992).

A sample has been drawn from one of two urns. One urn contains 70%

red balls and 30% white balls. The proportions are reversed in the other

urn. What is the probability that each of these samples was drawn from

the predominantly red urn?

A sample of three red balls and zero white balls (3R, 0W)

A sample of four red balls and three white balls (4R, 3W)

A sample of seven red balls and three white balls (7R, 3W)

The extensional target variable here is the degree of support for the ‘red’

hypothesis relative to the ‘white’ hypothesis. The normative solution is

straightforward: posterior probability (the target attribute) is determined

by an additive combination over sample elements – the difference be-

tween the number of red and white balls in the sample. The psychological

solution is equally straightforward: the prototype attribute (the heuristic)

is an average of support, which corresponds to the proportion of red balls

in the sample. Thus, the addition of (4R, 3W) to (3R, 0W) raises the value

of the target attribute but reduces the value of the heuristic attribute. This

particular example is fictitious, but the pattern of findings indicates that

respondents would derive much more confidence from (3R, 0W) than

from (7R, 3W) (Kahneman & Tversky, 1972; Griffin & Tversky, 1992).

• A  randomized clinical experiment was conducted as a follow-up to the

colonoscopy study described earlier. For half the patients, the instrument

was not immediately removed when the clinical examination ended.

Instead, the physician waited for about a minute, leaving the instrument

stationary. The experience during the extra period was uncomfortable,

but the procedure guaranteed that the colonoscopy never ended in severe

pain. Patients reported significantly more favorable global evaluations in

this experimental condition than in the control condition (Redelmeier,

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Katz, & Kahneman, in press). Violations of dominance have also been con-

firmed in choices. Kahneman, Fredrickson, Schreiber, and Redelmeier

(1993) exposed participants to two cold-pressor experiences, one with

each hand: a “short” episode (immersion of one hand in 14˚C water for 60

seconds), and a “long” episode (the short episode, plus an additional 30

seconds during which the water was gradually warmed to 15˚C). When

they were later asked which of the two experiences they preferred to re-

peat, a substantial majority chose the long trial. This pattern of choices is

predicted from the Peak/End rule of evaluation, which was described ear-

lier. The same pattern of results was found with unpleasant sounds of vari-

able loudness and duration (Schreiber & Kahneman, 2000).

The consistency of the results observed in diverse studies of prototype heuris-

tics suggests the need for a unified interpretation, and challenges interpreta-

tions that only apply to a single domain. A number of authors have offered

competing interpretations of base-rate neglect (Cosmides & Tooby, 1996;

Koehler, 1996), insensitivity to scope in WTP (Kopp, 1992), and duration neg-

lect (Ariely & Loewenstein, 2000). In general however, these interpretations

are specific to a particular task, and would not carry over to demonstrations

of extension neglect in the other tasks that have been discussed here.

Similarly, the attempts to describe the conjunction fallacy as a miscommuni-

cation between experimenter and respondent (Dulany & Hilton, 1991;

Hilton & Slugoski, 2001) do not explain analogous violations of monotonici-

ty in the cold-pressor experiment and in the pricing of private goods. In con-

trast, the account offered here (and developed in greater detail by

Kahneman & Frederick, 2002) is equally applicable to diverse tasks that re-

quire an assessment of an extensional target attribute. 

The findings obtained in choices and joint evaluations confirm the exis-

tence of two distinct ways of choosing, which were already identified in

prospect theory (Kahneman & Tversky, 1979). In the non-analytic procedure

that I have called “choosing by liking” (Kahneman, 1994), the individual con-

siders the global evaluation of the two options separately, and selects the one

that has the higher global value, without detailed comparison of the options.

Choice by global value was the basic mechanism assumed in prospect theory.

However, prospect theory also introduced the idea that if the individual de-

tects that one option dominates the other, the dominant option will be cho-

sen without consulting their separate valuations. The same mechanisms apply

to problems of judgment, such as the case of Linda, where some statistically

sophisticated individuals detect that one of the sets includes the other and re-

spond accordingly, ignoring representativeness. In Hsee’s dinnerware study

(1998), respondents chose by liking in separate evaluation, and chose by

dominance in joint evaluation. 

Joint evaluation is not sufficient to guarantee choice by dominance; it is al-

so necessary for the decision makers to realize explicitly that one of the op-

tions is strictly better than the other. This requirement was not satisfied in the

cold-pressor experiment. Although the participants were exposed to both ex-

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