strong associates will be judged to have occurredtogether frequently. According to this view
the illusory correlation betweensuspiciousness and peculiar drawing of the eyes
for example
is due tothe fact that suspiciousness is more readily associated with the eyes thanwith any other part of the body.Lifelong experience has taught us that
in general
instances of largeclasses are recalled better and faster than instances of less frequentclasses; that likely occurrences are easier to imagine than unlikely ones;and that the associative connections between events are strengthenedwhen the events frequently co-occur. As a result
man has at his disposal aprocedure (the availability heuristic) for estimating the numerosity of aclass
the likelihood of an event
or the frequency of co-occurrences
by theease with which the relevant mental operations of retrieval
construction
orassociation can be performed. However
as the preceding examples havedemonstrated
this valuable estimation procedure results in systematicerrors.Adjustment and AnchoringIn many situations
people make estimates by starting from an initial valuethat is adjusted to yield the final answer. The initial value
or starting point
may be suggested by the formulation of the problem
or it may be the resultof a partial computation. In either case
adjustments are typicallyinsufficient.18 That is
different starting points yield different estimates
which are biased toward the initial values. We call this phenomenonanchoring.Insufficient adjustment. In a demonstration of the anchoring effect
subjects were asked to estimate various quantities
stated in percentages(for example
the percentage of African countries in the United Nations).For each quantity
a number between 0 and 100 was determined byspinning a wheel of fortune in the subjectsâ presence. The subjects wereinstructed to indicate first whether that number was higher or lower than thevalue of the quantity
and then to estimate the value of the quantity bymoving upward or downward from the given number. Different groups weregiven different numbers for each quantity
and these arbitrary numbers hada marked effect on estimates. For example
the median estimates of the
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