Thinking and Deciding

140 DESCRIPTIVE THEORY OF PROBABILITY JUDGMENT
Figure 6.2: Typical pattern of results for a subject’s judgment being correct as a
function of the subject’s confidence that the judgment is correct.
nize correct spellings rather than to produce them (Adams and Adams, 1960). In
other cases, though, overconfidence at the right side of the graph (high-confidence)
is extreme. In one cross-cultural study, subjects answered a general-knowledge questionnaire
with items such as “When did the People’s Republic of China join the U.N.:
1971 or 1972?” or “What is the capital of New Zealand: Auckland or Wellington?”
Subjects also indicated their confidence as a probability. All of the items had two
choices for answers, so subjects could score 50% correct by guessing; a confidence
level lower than 50% was therefore never warranted. College students from Hong
Kong and Malaysia were correct only about 65% of the time when they said that
they were 100% certain of being correct. (The probability judgments of Indonesian
students were even more poorly calibrated.) British students’ answers were considerably
better calibrated; they scored about 78% correct when they said that they were
100% certain. These differences are not the result of differences in knowledge about
the questions: Rather, the British subjects were more cautious, using the 100% category
far less often, so that they were more likely to be correct when they did use it.
The researchers suggested that cultural differences affect the way that people think
about probability (Wright, Phillips, Whalley, Choo, Ng, Tan, and Wisudha, 1978;
see also Wright and Phillips, 1980).
Fischhoff, Slovic, and Lichtenstein (1977) examined a number of possible explanations
of the basic finding of overconfidence for high-confidence judgments. They
used items like those employed by Wright and his colleagues (for example, “Absinthe
is: a liqueur or a precious stone?”), as well as other kinds of items — for
example, items in which subjects had to indicate which cause of death was more
common in the United States (for example, appendicitis, or pregnancy, abortion, and