Daniel Kahneman Nobel Lecture

477

In light of the findings discussed in the preceding section, it is useful to

consider situations in which people will not neglect extension completely.

Extension effects are expected, in the present model, if the individual (i) has

information about the extension of the relevant set; (ii) is reminded of the

relevance of extension; and (iii) is able to detect that her intuitive judgments

neglect extension. These conditions are least likely to hold – and complete

neglect most likely to be observed – when the judge evaluates a single object

and when the extension of the set is not explicitly mentioned. At the other ex-

treme, the conditions for a positive effect of extension are all satisfied in psy-

chologists’ favorite research design: the within-subject factorial experiment,

in which values of extension are crossed with the values of other variables in

the design. As noted earlier, this design provides an obvious cue that the ex-

perimenter considers every manipulated variable relevant, and it enables par-

ticipants to ensure that their judgments exhibit sensitivity to all these vari-

ables. The factorial design is therefore especially inappropriate for testing

hypotheses about biases of neglect (Kahneman & Frederick, 2002).

In spite of these objections, within-subject factorial designs have been used

in several experimental studies of extension neglect. Figure 10 illustrates the

remarkably consistent additive extension effect that has emerged in these exper-

iments (Schreiber & Kahneman, 2000). In each of the experiments, the ex-

tension variable has a slight but significant effect, and combines additively

with other information. The additivity is noteworthy, because it is normative-

ly inappropriate. For each panel of Figure 10, a compelling normative argu-

ment can be made for a quasi-multiplicative rule in which the lines should 

fan out.

4

The observed pattern is compatible with a process of anchoring and

adjustment: the intuitive judgment provides an anchor, and small adjust-

ments from that anchor are made to accommodate the role of extension. 

Patient A

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Figure 9. Pain intensity reported by two colonoscopy patients.

4

Anderson (1996, p. 253) has described several other situations in which variables that should be

combined multiplicatively are combined additively.

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478

Tests of monotonicity

Extensional variables, like sums, obey monotonicity. The sum of a set of posi-

tive values is at least as high as the maximum of its subsets. In contrast, the

average of a subset can be higher than the average of a set that includes it.

Violations of monotonicity are therefore bound to occur when an extension-

al attribute is judged by a prototype attribute: it must be possible to find 

cases in which adding elements to a set causes the judgment of the target vari-

able to decrease. This test of prototype heuristics is less demanding than the

hypothesis of extension neglect, and violations of monotonicity are compatib-

le with some degree of sensitivity to extension (Ariely & Loewenstein, 2000).

Nevertheless, violations of monotonicity in important tasks of judgment and

choice are the strongest source of support for the hypothesis that prototype 

attributes are substituted for extensional attributes in these tasks. 

• Conjunction errors, which violate monotonicity, have been demonstrated

in the Linda problem and in other problems of the same type. There are

no documented exceptions to the predicted pattern when the judgments

are obtained in a between-subjects design, or when the two critical out-

Figure 10. (a) Willingness to pay to restore damage to species that differ in popularity as a

function of the damage they have suffered (from Kahneman, Ritov, & Schkade, 1999); (b)

Global evaluations of aversive sounds of different loudness as a function of duration for

subjects selected for their high sensitivity to duration (from Schreiber & Kahneman, 2000);

(c) Ratings of probability for predictions that differ in representativeness as a function of

base-rate frequency (from Novemsky & Kronzon, 1999); (d) Global evaluations of episodes

of painful pressure that differ in temporal profile as a function of duration (Ariely, 1998).

 

Ariely Data

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Nov emsky & Kronzon Data

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