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Psychological
Review
1988,
Vol.
95, No.
3,371-38'
Copyright
1988
by the
American
Psychological
Association,
Inc.
0033-295X/88/S00.75
Contingent
Weighting
in
Judgment
and
Choice
Amos
Tversky
Shmuel
Sattath
Stanford
University Hebrew
University,
Jerusalem,
Israel
Paul
Slovic
Decision
Research,
Eugene, Oregon
and
University
of
Oregon
Preference
can be
inferred
from
direct choice between options
or
from
a
matching procedure
in
which
the
decision maker
adjusts
one
option
to
match another. Studies
of
preferences
between
two-
dimensional
options (e.g., public policies,
job
applicants,
benefit
plans)
show
that
the
more promi-
nent
dimension looms larger
in
choice than
in
matching. Thus, choice
is
more lexicographic than
matching. This
finding is
viewed
as an
instance
of a
general principle
of
compatibility:
The
weighting
of
inputs
is
enhanced
by
their compatibility with
the
output.
To
account
for
such
effects,
we
develop
a
hierarchy
of
models
in
which
the
trade-off
between
attributes
is
contingent
on the
nature
of the
response.
The
simplest theory
of
this type, called
the
contingent weighting model,
is
applied
to
the
analysis
of
various compatibility
effects,
including
the
choice-matching discrepancy
and the
preference-reversal
phenomenon. These results raise both conceptual
and
practical questions
con-
cerning
the
nature,
the
meaning
and the
assessment
of
preference.
The
relation
of
preference
between acts
or
options
is the key
element
of
decision theory that provides
the
basis
for the
mea-
surement
of
utility
or
value.
In
axiomatic treatments
of
decision
theory,
the
concept
of
preference
appears
as an
abstract
relation
that
is
given
an
empirical interpretation through
specific
meth-
ods of
elicitation,
such
as
choice
and
matching.
In
choice
the
decision maker
selects
an
option
from
an
offered
set of two or
more alternatives.
In
matching
the
decision
maker
is
required
to
set the
value
of
some variable
in
order
to
achieve
an
equivalence
between
options (e.g., what chance
to win
$750
is as
attractive
as 1
chance
in 10 to win
$2,500?).
The
standard analysis
of
choice assumes procedure invari-
ance: Normatively equivalent procedures
for
assessing
prefer-
ences should
give
rise
to the
same preference order. Indeed, the-
ories
of
measurement generally require
the
ordering
of
objects
to be
independent
of the
particular method
of
assessment.
In
classical
physical
measurement,
it is
commonly assumed that
each
object possesses
a
well-defined
quantity
of the
attribute
in
question (e.g., length, mass)
and
that
different
measurement
procedures elicit
the
same ordering
of
objects
with
respect
to
this
attribute. Analogously,
the
classical theory
of
preference
assumes
that
each individual
has a
well-defined
preference
or-
der (or a
utility
function)
and
that
different
methods
of
elicita-
tion
produce
the
same ordering
of
options.
To
determine
the
heavier
of two
objects,
for
example,
we can
place them
on the
two
sides
of a pan
balance
and
observe which side goes down.
Alternatively,
we can
place each object separately
on a
sliding
scale
and
observe
the
position
at
which
the
sliding scale
is
bal-
anced. Similarly,
to
determine
the
preference order between
op-
tions
we can use
either choice
or
matching.
Note
that
the pan
This
work
was
supported
by
Contract
N00014-84-K-0615
from
the
Office
of
Naval
Research
to
Stanford University
and by
National
Sci-
ence
Foundation
Grant
5ES-8712-145
to
Decision Research.
The
article
has
benefited
from
discussions with Greg Fischer, Dale
Griffin,
Eric Johnson, Daniel
Kahneman,
and
Lcnnart
Sjtiberg.
balance
is
analogous
to
binary choice, whereas
the
sliding scale
resembles matching.
The
assumption
of
procedure invariance
is
likely
to
hold
when
people have well-articulated preferences
and
beliefs,
as is
commonly assumed
in the
classical theory.
If one
likes opera
but not
ballet,
for
example, this preference
is
likely
to
emerge
regardless
of
whether
one
compares
the two
directly
or
evalu-
ates them independently. Procedure invariance
may
hold
even
in
the
absence
of
precomputed
preferences,
if
people
use a
con-
sistent algorithm.
We do not
immediately
know
the
value
of
7(8 + 9), but we
have
an
algorithm
for
computing
it
that yields
the
same
answer
regardless
of
whether
the
addition
is
performed
before
or
after
the
multiplication. Similarly, procedure invari-
ance
is
likely
to be
satisfied
if the
value
of
each option
is
com-
puted
by a
well-defined
criterion, such
as
expected utility.
Studies
of
decision
and
judgment,
however,
indicate
that
the
foregoing
conditions
for
procedure invariance
are not
generally
true
and
that people
often
do not
have
well-defined
values
and
beliefs
(e.g.,
Fischhoff,
Slovic
&
Lichtenstein,
1980; March,
1978;
Shafer
&
Tversky, 1985).
In
these situations, observed
preferences
are not
simply
read
off
from
some master list; they
are
actually constructed
in the
elicitation
process.
Furthermore,
choice
is
contingent
or
context sensitive:
It
depends
on the
fram-
ing
of the
problem
and on the
method
of
elicitation (Payne,
1982;
Slovic
&
Lichtenstein, 1983; Tversky
&
Kahneman,
1986).
Different
elicitation procedures highlight
different
as-
pects
of
options
and
suggest alternative heuristics, which
may
give
rise
to
inconsistent responses.
An
adequate account
of
choice,
therefore,
requires
a
psychological analysis
of
the
elicita-
tion
process
and its
effect
on the
observed response.
What
are the
differences
between
choice
and
matching,
and
how
do
they
affect
people's responses? Because
our
understand-
ing
of the
mental processes involved
is
limited,
the
analysis
is
necessarily sketchy
and
incomplete. Nevertheless, there
is
rea-
son
to
expect
that
choice
and
matching
may
differ
in a
predict-
able
manner. Consider
the
following
example. Suppose Joan
371
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