Thinking and Deciding

METHODS FOR EMPIRICAL RESEARCH 41
Individual differences
Differences among people are of interest for many reasons. If some people show a
bias and others do not, we can look for both causes and effects of these differences.
For example, some of the difficulties that people have with decisions about risks,
or present/future conflict, are correlated with measures of “cognitive reflection,” as
measured by the ability to solve trick problems such as: “A bat and a ball cost $1.10
in total. The bat costs $1 more than the ball. How much does the ball cost?” (Frederick,
2005).
Similarly, Peters and her colleagues (2006) assessed numeracy with questions
such as: “The chance of getting a viral infection is .0005. Out of 10,000 people, about
how many of them are expected to get infected?” Subjects who gave more correct
answers to questions like this made better decisions and judgments when numbers
were involved. For example, they were more likely to bet on drawing a red jelly bean
from a bowl when the bowl contained 1 red bean out of 10 than when it contained
9 out of 100. Together, these results suggest that some biases can be overcome by
types of quantitative thinking that are within the capacity of a fair number of people.
(See also p. 212.)
More generally, studies of individual differences in biases have repeatedly found
that many people do not show biases. A “bias” is a departure from the normative
model in a particular direction. Thus, if half of the subjects show a bias and the
other half show no bias in either direction, the average subject will show a bias. With
enough subjects, the overall average bias will be statistically reliable. It is important
to determine whether biases are universal or not. Some have compared judgment
biases to optical illusions, which enlighten us about how our visual system works
by showing how it systematically fails in some cases. This analogy is a poor one if
only half of the people show a bias. Everyone with normal vision sees most visual
illusions. Visual illusions may be hard wired into our nervous systems in ways that
judgment biases are not.
Another reason for studying individual differences is that some people may show
the reverse of the usual bias. If these people are sufficiently rare, then the usual bias
will still be found on the average, but, really, there would be two biases going in
different directions.
Cultural differences can also enlighten us about the range of human possibility.
Individual differences may result from education, subcultural differences, or genetic
differences. They may affect people’s success or failure in achieving various goals.
Research on differences among people is based on correlations, that is, observation
of differences rather than experimental manipulation. Because of this, it is often difficult
to determine what the cause of some difference is, or whether it is responsible
for some effect. For example, sex differences could result from genetic or environmental
causes. Still, such research is often useful.