PSYCHOLOGICAL SCIENCE
Research Report
VAGUENESS, AMBIGUITY, AND THE COST OF
MUTUAL UNDERSTANDING
Ido Erev,' Thomas S. Wallsten," and Martha M. NeaP
Department of Industrial Engineering and Management, The Technion—Israel Institute of Technology, and
^Department of Psychology, The University of North Carolina at Chapel Hill
Abstract—We suggest that vague and
ambiguous natural language is commonly used to serve the needs of the linguistic community. Specifically, some
social dilemmas can be solved by variability in the participants' behavior,
which will occur among self-interested
individuals only if they differentially interpret available information. Because
imprecise communications are not understood identically by everyone, they
benefit society in certain situations by
facilitating heterogeneous choices. An
experiment demonstrates that the frequency of vague communication increases in a controlled social setting
when its use is beneficial for the group.
It is widely believed that clarity of expression is always desirable and that mutual understanding is necessarily in the
best interests of society. In contrast with
this belief is the widespread use of ambiguous and vague expressions that create misunderstanding. A statement or a
word is defined as ambiguous if it is capable of being understood in two or more
different, but precise, ways. It is said to
be vague if it is not clearly defined or
cannot be interpreted in at least one precise way (Black, 1937; Wallsten, 1990).
One explanation for the inconsistency
between the assumed goal of communication and the imprecision inherent in
much of natural language is that language
serves multiple conflicting goals (Slobin,
1979) and the production cost of precision (in terms of time, effort, and loss of
expressiveness) often exceeds its benefits.
Alternatively, we suggest that precise
communications are not always desirable. Rather, vagueness or ambiguity
may be necessary under some circumAddress all correspondence to: Prof.
Thomas S. Wallsten, Department of Psychology, The University of North Carolina at
Chapel Hill, Chapel Hill, NC 27599-3270.
VOL. 2, NO. 5, SEPTEMBER 1991
stances to maximize a society's collective gain or possibly to ensure its longterm existence. We make this argument
first from a social-ecological perspective. Then we report an experiment that
demonstrates that the frequency of
vague communication increases with experience in a situation in which imprecision is socially useful.
A primary assumption underlying
much social and some biological theory,
which we accept, is that organisms are
self-interested. That is. they behave as if
they try to maximize long-term expected
reward. Nevertheless, there must be
some limits on the organism's ability to
maximize self-interest, because in some
situations the collective result of individually rational behavior is the destruction
of the group. Such situations are called
social dilemmas.
The classic example of a social dilemma was described by Lloyd (1833)
(see also Hardin. 1968) as the problem of
the commons: Each of a number of shepherds owns 10 sheep grazing on a common pasture. An individual who adds an
11th sheep to the common increases personal wealth, while the loss resulting
from the reduced food supply per animal
is shared by all the shepherds. Hence,
self-interested individuals should add
sheep, and the dilemma occurs because
the commons is thereby rapidly destroyed.
Some social dilemmas, which might
be called variability dilemmas, can be
solved naturally by the use of vague or
ambiguous communications. This solution may not help in the problem of the
commons, but imagine another dilemma
Lloyd's shepherds may face. Perhaps after a few happy years of sharing the commons, the group faces a drought that
forces it to move to a new location with
water. Only a few routes are available
and it is known that all but one will be
blocked by wolves that will kill all the
sheep passing their way, A scout is sent
to observe the wolves in order to predict
their location during the group's migration. Clearly, the scout can only form an
uncertain prediction of which route will
be open. If this information is presented
precisely (e.g., as numerical estimates of
the chances of succeeding on each
route), and if all the shepherds are rational, they will all select the same (highest
probability) route. It is easy to see that
such consistency in the shepherds' behavior is not in the group's best interests. Variability in the shepherds'
choices is necessary to maximize the
chances that at least one shepherd will
reach the water and that the society will
survive. One way to induce this variability among self-motivated individuals is to
communicate the information in vague
terms that people interpret differently.
Then, each individual will choose the
route he or she deems safest, and collectively the group wil! benefit. Crucial to
this argument is the existence of large
individual differences in understanding
such expressions (Beyth-Marom, 1982;
Budescu & Wallsten. 1985; Wallsten,
Budescu, & Erev, 1988).
It must be noted that often in the absence of explicit communication strategies, people differentially receive or interpret available infonnation so that, to
society's gain, they select diverse actions for achieving the same goal. An obvious example is the stock market, in
which behavioral variance over individuals is crucial for the market's stability
and growth. Consistent with this claim,
Sloan and Stem (1988) have suggested
that one of the reasons for the 1987 stock
market crash was the uniform behavior
of large-scale investors stemming from
computer-based strategies utilizing precise real-time information. It appears
that some imprecision in information and
its interpretation is needed to keep the
world economy sound.
The examples presented above suggest that in interactions among selfmotivated individuals, imprecise information can be used to solve variability
Copyright © 1991 American Psychological Society
321
PSYCHOLOGICAL SCIENCE
The Cost of Muiiial Uiiderslanding
dilemmas. Thus, the hypothesis is suggeslcd Ihat amhigtiotis or vague communications are used when they benefit the
group. The remainder of this paper presents and discusses an experiment that
was designed to examine this hypothesis
in a controlled social setting.
The experiment used groups of six
subjects in which (on a revolving basis
over 42 trials) one was the advisor, three
were decision-makers (DMs), and two
were observers. On each trial, the advisor communicated information to the
DMs. who made choices from which
both they and the other society members
(the advisor and the two observers)
stood to gain. The optimal strategy for all
three DMs individually always was to select the highest expected value (EV) alternative. This strategy also benefited
the other society members in the control
condition. However, the experimental
condition presented a variability dilemma, in that the group was best served
by heterogeneous DM choices. The experimental question was whether the frequency of vague communications would
increase with experience in the experimental condition relative to the control
condition.
METHOD
Subjects (120 Introductory Psychology students at the University of North
Carolina) were run in groups of six in a
single room with a personal computer
and arrangements to ensure that the
DMs" choices could be made privately.
Ten groups of subjects served in each of
two conditions. Conversation was not
permitted beyond that required for the
task, as described below.
Written instructions described the experimental game the group was to play
on the computer. The instructions also
stated that each player received $3 for
showing up, and could eam more money
or lose part of this amount in the game.
The exact profits were updated on the
computer screen and all the players
could see them at the end of each round.
To begin each trial, one player was
designated as the advisor and was seated
next to the computer screen, three others were the DMs and were given decision forms, and the remaining two were
the observers. A participation fee was
subtracted from each player's total prof322
its (with the exact amount depending on
ihc" player's role and the payoff condition, as will be explained below). The
screen was then turned so that only the
advisor could see It. and a three-color
spinner, illustrated in Figure lA. was
displayed. The advisor was required to
describe the chances that this spinner
would land on each of its colors by
choosing a probability expression for
each of the possible events from a list of
eight unique terms for each color, as illustrated in Figure IB.
Each DM then circled one of the colors noted on his or her decision form, an
example of which is shown in Figure IC
for the spinner in Figure lA, and gave
the form to the experimenter. The experimenter entered the decisions in the computer, then the spinner was spun seven
times and profits were calculated.
After each round the players changed
roles, so that each served as advisor
seven times (once in each block of six
trials) and as DM 21 times. Approximately the same six spinners appeared in
each block (the sector areas were perturbated by a small random error component each time), with each advisor seeing
each spinner at least once.
The terms available for selection by
the advisor depended on the spinner proportions. In all cases, four of them were
integer percentages, randomly selected
from the five values in the range (real
percentage - 2%. real percentage -f2%). The other four terms were vague
verbal phrases randomly chosen from a
hst of 18 low expressions if the objective
proportion was below .20. and from a list
of 26 higher phrases otherwise.'
1. The high-probability phrases: likely,
good chance, decent chance, probable, quite
probable, quite likely, very good chance, high
probability, fair chance, fairly likely, not too
bad. even chance, somewhat likely, maybe,
possible, decent chance, OK chance, passable chance, medium chance, fairly possible.
some what good, fairly good chance, pretty
good chance, relatively good, acceptable
chance, quite possible.
The low-probability phrases: very unlikely, improbable, very improbable, almost
impossible, impossible, not likely, low
chance, very small chance, no chance, extremely unlikely, terrible chance, no way,
slim chance, very slim chance, very poor
chance, extremely poor chance, poor chance.
very small section.
The DMs' participation fee was always 50^, and they earned the amount
written next to their selected color each
time it was landed upon out of the seven
spins. The fees and payoff contingencies
for the advisors and the observers depended on which of the two conditions
they were in. In the experimental condition, the participation fee was $1 for the
advisor and 50C for the observers. In
turn, the advisor earned 200 and each observer earned 10? for each of the seven
spins landing on a color that was chosen
by at least one of the DMs. In the control
condition, the game participation fee was
70C for the advisor and 350 for the observers. In this case, the advisor earned
200 and each observer earned 100 each
time the spinner landed on a color that
was chosen by all three DMs.
The participation fees, spinner probabilities, and payoff values were selected
so that (1) the DM would always have to
choose the highest HV (= probability x
outcome x 7) alternative to avoid a personal expected loss; (2) in the experimental condition, variability in the DMs'
choices would be required to prevent expected losses for the advisor and the observers; and (3) in the control condition,
only consistent choices of the highest
EV alternative by the DMs would shield
the advisor and the observers from expected losses. Moreover, spinner proportions (observed by the advisor) and
DM payoffs (on the DM form) were arranged so that on each trial, the altemative with the highest probability was the
only one with EV above 500 for the DM.
On half of the trials, this altemative also
had a higher value than the one with the
second highest EV. The alternative with
the lowest probability always had the
lowest EV.
In addition to the regular earnings,
bonuses of $3, $2, and $1 were promised
in the experimental condition to the subjects who earned the first, second, and
third highest profits, respectively. These
bonuses were introduced to decrease the
chance that groups would arrive at the
session with a preplanned cooperative
strategy.
To summarize, contingencies and
payoffs were arranged so that it was always in the DM's self-interest to select
the most probable color. It was in the
advisors' and the observers' interest for
the DMs to agree on their color selection
VOL. 2, NO. 5, SEPTEMBER 1991
PSYCHOLOGICAL SCIENCE
ido Erev, Thomas S. Wallsten, and Martha M. Neal
05
Exporimenlal
Conlrol
0.4-
0.3-
0.2-
O.V
B. Phrases
YELLOW:
GREEN:
RED:
0.0-t-
even chance
36%
34%
not too bad
relatively good
good chance
33%
35%
7%
unlikely
5%
very slim chance
no way
9%
not likely
6%
57%
probable
maybe
very good chance
61%
59%
60%
likely
C. Decision Form
Yellow
Red
Green
-
$.19
$.17
$.15
Fig. L The spinner, the available phrases, and the decision form in one of the rounds.
in the control group, but to make heterogeneous choices in the experimental
group.
RESULTS
An advisor's description of a spinner
was classified as vague if he or she used
verbal terms to describe at least two of
its sections. Figure 2 shows the proportion of vague descriptions as a function
of block number in each condition. Over
groups (using trial as a unit of analysis)
the linear increase in the proportion of
v^ue descriptions is significant in the
experimental condition (r = .66. p <
.0001), but not in the control condition (r
VOL. 2, NO. 5, SEPTEMBER 1991
= .14, p > .3). The difference between
the linear trends in the two conditions is
also significant f/(41) = 3.7,/? < .001]. In
the experimental condition, the proportion of vague descriptions increased with
experience in 9 of the 10 groups (significantly so in four of them,/7 < .05). In the
control condition, the proportion increased in 6 of the 10 groups, but never
significantly.^
2. A reviewer suggested that in the experimental condition, advisors may have selected
phrases not to provide vague accurate descriptions, but to confuse or mislead DMs. As
a check on this possibility, five new subjects
were asked to provide numerical interpreta-
1
2
3
4
5
Block Number
Fig. 2. Proportion of vague assessments
as a function of experience (experimental block) in the two conditions.
The use of vague descriptions benefited the advisor and observers in the experimental condition, but not in the control condition. Their mean profit given
vague descriptions minus that given precise ones was positive in the experimental condition (M = 100 per trial, p < .05)
and negative in the control condition (M
= -360. p < .01). The interaction between the description type and the condition was significant [F(\S, 1) = 24.6, p
< .0001].
DISCUSSION
The use of vague discriptors increased when variable DM behavior was
in the group's collective interest, but not
otherwise. These results support the hypothesis that vague communication develops in a group to solve a variability
dilemma.
tions of the high phrases. The mean of these
numerical translations had a linear correlation
off - .71 (p < .0001) with the probabilities of
the sectors the phrases were used to describe,
suggesting that advisors were attempting to
convey correct information. To avoid a spuriously high correlation, low phrases were not
included in this analysis.
323
PSYCHOl.OGICAL SCIENCE
The Cost of Mutual Understanding
It is easy to think of other situations
in which society is best served by vague
or ambiguous communications. For example. negotiiUions between groups wilh
conflicting interests sometimes are
solved with agreements that each side
can naturally interpret in its own way.
Such observations in conjunction with
the present results suggest Ihat mutual
understanding is not always the ideal
goal and that users of natural language
may avoid it for reasons other than excessive production costs. To account for
such phenomena, theories of language
should consider the needs of the linguistic community as well as those of the individual.
In this regard, it is of interest to ask
whether natural languages become less
precise as they evolve. For example,
pidgin languages, which emerge when
two groups of different linguistic backgrounds interact, have simple grammati-
cal structures that increase in complexity
as the language develops (creolizes)
(Smith. 1973), Does the frequency of
vague or ambiguous cxpression.s increase simultaneously, perhaps because
imprecise communications provide a
means for solving variability dilemmas'?
Acknowledgments—This paper was supported by a tJNC Cognitive Science grant
and by Grant BNS 8908554 from the U.S.
National Science Foundation, We thank
Samuel Fillenbaum and William Lycan for
helpful comments.
REFERENCES
Beyth-Marotn, R. (1982). How probable is probable?
A numerical translation of verbal probability
expressions. Journal of Forecasting, I, 257269.
Black, M. (1937), Vagueness. Philosophy of Science. 4. 427^55.
Budescu, D.V. , & Wailsten, T.S. (1985). Consistency in interpretation ofprobabilrstie phrases,
Ori^einizalional Beha vior and Human Decision
Processes, 36. 39M05.
Hardin, C R , (1968), The tragedy of the eommons.
Science. 162. 1243-1248.
Lloyd, W.F. (1833). Tn'o lectures on the checks to
population. Oxford: Oxford University Press.
Sloan, A,, & Stern, R.L. (1988), How Vo = V.Mrf,)
- ^le^Nidi) led to Black Monday, Forbes,
141. 55-59.
Slobin, D,I. (1979). FsychoUnguistics.
Glenview,
IL; Seott, Foresman.
Smith, D.M, (1973). Creolrzalion and language ontogeny; A preliminary paradigm for comparing
language socialization and language acculturation. In C.-J.N. Baily & R.W. Shuy (Eds,),
New ways of analyzing variation in English
(pp, 287-296), Washington, DC: Georgetown
University Press,
Wallsten, T.S. (1990), The costs and benefits of
vague information. In R. Hogarth (Ed,). Insights in decision making: Theory and applications. A tribute to the late Hillel Einhorn
(pp. 28-43). Chicago: University of Chicago
Press.
Wallsten, T.S,. Budescu, D.V.. & Erev, 1, (1988).
Understanding and using linguistic uncertainties, Acta Psychologica, 68. 39-52.
(RECEIVED 12/5/90; ACCEPTED 3/26/91)
American Psychological Society
The American Psychological Society was founded in 1988 as an independent,
multipurpose organization to advance the discipline of psychology, to preserve
the scientific base of psychology, to promote public understanding of psychological science and its applications, to enhance the quality of graduate education, and to encourage the "giving away" of psychology in the public interest.
All members of the American Psychological Society receive Psychological Science and the APS Observer as part of their annual membership dues, which are
$75.00 per year through 1991. For membership information and applications
contact the American Psychological Society, Suite 345, 1511 K Street, NW,
Washington, DC 20005, Telephone: 202-783-2077; Fax 202-783-2083; Bitnet:
APSAGK(tlUMUC or
324
VOL, 2, NO, 5, SEPTEMBER 1991