Thinking and Deciding

190 JUDGMENT OF CORRELATION AND CONTINGENCY
Table 8.3: Incidence of response and outcome for 120 trials
Outcome
Response Score No score
A 48 12
B 48 12
some control over the outcome even when they have no control at all has come to be
called the illusion of control.
These results were obtained despite the fact that subjects were explicitly instructed
that “control means the ability to produce the No Score light as well as
to produce the Score light.” Subjects were also explicitly warned that there might
be no relation at all between their responses and the outcomes. The same results
were obtained in the judgments of subjects who merely watched other subjects do
the experiment. Therefore, we cannot explain the results in terms of some effect of
the choice itself; the “spectator” subjects made no choices. The results were also
obtained when subjects were explicitly asked to try to “control” the outcome rather
than to “score”; these “control” subjects had to say aloud, in advance, which light
they were trying to produce.
In a questionnaire given after the experiment, subjects were shown tables of outcomes
similar to Table 8.3. The figures in this table reveal that the Score light came
on with a probability of .8 regardless of the response. Once again, even with the
tables before them the subjects judged their degree of control in terms of the probability
of success rather than in terms of the difference in results produced by the two
buttons.
Part of the subjects’ difficulty seemed to result from the fact that they had to press
one button on each trial. When they were asked how much “control” they had over
the outcome, they tended to assume that they had a fair amount, because, they reasoned,
if they had not pushed any button, there would have been no outcome. Allan
and Jenkins (1980) tried the procedure with a single button. The subjects could press
or not press on each trial, and after 100 trials the subjects were asked to estimate the
degree of influence they had, or the degree of connection between pressing the button
and the outcome. In this procedure, subjects still showed the illusion of control.
They still said they had some control (influence or connection) over the outcome,
even when they actually had none. The illusion was smaller with one button than
with two, however. Subjects tended to give lower ratings of their degree of control.
In this study, subjects’ ratings were affected by the actual amount of control; subjects
estimated that they had more control in a .9 − .1 condition (outcome appears with
probability .9 when they press, .1 when they do not press) than in a .9 − .5 condition.
With either one button or two, however, they thought they had more control in a