Daniel Kahneman Nobel Lecture

of a particular value of the target attribute. On the other hand, the definition

of the concept of heuristic by the process of attribute substitution greatly ex-

tends its range of application.

For a perceptual example of attribute substitution, consider the question:

“What are the sizes of the two horses in Figure 7, as they are shown on the

page?” The images are in fact identical in size, but the figure produces a com-

pelling illusion. The target attribute that the observer is instructed to report

is two-dimensional size, but the responses actually map an impression of

three-dimensional size onto units of length that are appropriate to the re-

quired judgment. In the terms of the model, three-dimensional size is the

heuristic attribute. As in other cases of attribute substitution, the illusion is

caused by differential accessibility. An impression of three-dimensional size is

the only impression of size that comes to mind for naïve observers – painters

and experienced photographers are able to do better – and it produces a per-

ceptual illusion in the judgment of picture size. The cognitive illusions that

are produced by attribute substitution have the same character: an impres-

sion of one attribute is mapped onto the scale of another, and the judge is

normally unaware of the substitution.

Direct tests of attribute substitution

An experiment described by Kahneman and Tversky (1973) illustrates a cog-

nitive illusion that arises from attribute substitution. It also illustrates a par-

ticularly strict test of the hypothesis of substitution, in a research paradigm

that Kahneman and Frederick (2002) labeled the heuristic elicitation design.

Participants were given the following description of a fictitious graduate stu-

dent, which was shown along with a list of nine fields of graduate specializa-

tion.

Tom W. is of high intelligence, although lacking in true creativity. He

has a need for order and clarity, and for neat and tidy systems in which

every detail finds its appropriate place. His writing is rather dull and

mechanical, occasionally enlivened by somewhat corny puns and by

flashes of imagination of the sci-fi type. He has a strong drive for com-

petence. He seems to have little feel and little sympathy for other peo-

ple and does not enjoy interacting with others. Self-centered, he

nonetheless has a deep moral sense. (p.127)

Participants in a representativeness group ranked the nine fields of specializa-

tion by the degree to which Tom W. “resembles a typical graduate student”

(in that field). Participants in a base-rate group evaluated the relative fre-

quencies of the nine fields of graduate specialization. The description of Tom

W. was deliberately constructed to make him more representative of the less

populated fields: the rank correlation between the averages of representa-

tiveness rankings and of estimated base rates was -.65. Finally, participants in

the  probability group ranked the nine fields according to the likelihood of

Tom W.’s specializing in each. These respondents were graduate students in

psychology at major universities. They were given information that was in-

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tended to discredit the evidence of the personality sketch, namely that it had

been written by a psychologist when Tom W. was in high school, on the basis

of personality tests of dubious validity. 

A description based on unreliable information should be given little

weight, and predictions made in the absence of valid evidence should revert

to base rates. Statistical logic therefore dictates that the correlation between

judgments of probability and of representativeness should be negative in this

problem. In contrast, the hypothesis of attribute substitution implies that the

ranking of fields by the two measures should coincide. The results are shown

in Figure 7. The correlation between the mean judgments of representative-

ness and of probability is nearly perfect (.97), supporting attribute substitu-

tion. 

Another study in the same design involved one of the best-known charac-

ters in the heuristics and biases literature.

Linda is 31 years old, single, outspoken and very bright. She majored in

philosophy. As a student she was deeply concerned with issues of dis-

crimination and social justice and also participated in antinuclear

demonstrations.

Respondents were shown the description of Linda and a list of eight possible

outcomes describing her present employment and activities. The two critical

items in the list were #6 (“Linda is a bank teller”) and the conjunction item

#8 (“Linda is a bank teller and active in the feminist movement”). The other

six possibilities were unrelated and miscellaneous (e.g., elementary school

teacher, psychiatric social worker). As in the Tom W. problem, some respon-

dents ranked the eight outcomes by representativeness; others ranked the

same outcomes by probability. The correlation between the mean rankings

was .99. Furthermore, the proportion of respondents who ranked the con-

junction (item #8) higher than its constituent (#6) was about the same for

representativeness (85%) and for probability (89%). The ordering of the two

items is quite reasonable for judgments of similarity: Linda does resemble the

Linda

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m e an  r ank   (s im ilar ity)

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Tom  W .

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mean rank (likelihood)

Figure 8.

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