Judgment and Decision Making in Information Systems
Group Judgment and
Decision Making
Yuval Shahar M.D., Ph.D.
Group Decision Making
• Essentially, an extension of individual decision
making with all faults and biases
• Unique features: Social influence, mutual
discussion, a group decision-making procedure
• Process and mode of decision making (e.g.,
interactive discussion, majority vote) are crucial
• Advantages: Potential brainstorming, multiple types
of expertise and points of view, facilitation of
problem solving and creativity
• Disadvantages: Social loafing, conformity,
polarization of previous opinions, “groupthink”
phenomenon might lead to unreasonable decisions
Are N+1 Heads Better than One?
• Groups are often better in solving problems, especially involving
unfamiliar domains
– Example: The NASA moon landing survival experiment (ranking of
15 items by degree of importance): The group error is much smaller
than the average of the personal errors
• Review studies show that improvement occurs in several different areas:
– Quantitative judgment (up to 23 to 32% accuracy increase)
– Brain teasers and logic problems (better then average)
– General knowledge questions (better than average member)
– Creativity and problem solving (groups can pool resources)
• However, it is not clear that the group interaction is useful:
– The best individual usually outperforms the group as a whole in all types
of judgments [Hastie, 1986] and their accuracy is even reduced!
– brainstorming is more effective when ideas are generated independently
and later combined, than when conducted in a group session [Hill, 1982]
(might include a “social loafing” element as well)
Conformity
[Asch, 1951, 1955, 1956]
• Is the test line equal in length to A, B, or C?
• Small (3 of 4) majorities are sufficient to elicit
substantial conformity with a wrong result
• Any opposition can have a major effect; even a single
dissenting individual can nullify the effect!
Test line
A
B
C
Asch Results: The Pressure to Conform
Condition
Error rate
Subject is alone
1%
With 1 person who says “A”
3%
With 2 persons who say “A”
13%
With 3 persons who say “A”
33%
With 6 persons who say “A”
and 1 person who says “B”
6%
Groupthink
[Janice, 1982]
• “A deterioration of mental efficiency, reality
testing and moral judgment that results from ingroup pressures”
• Famous examples: Bay of Pigs invasion;
Challenger space shuttle launch; Israel before the
October 1973 war; etc.
• Occurs when groups are cohesive and insulated
from the outside, while inside pressures for group
loyalty and conformity lead to muddled thinking
Groupthink Symptoms [Janice 1982]
• Illusion of invulnerability leads to unjustified
optimism and risk taking
• Collective efforts to discount warnings
• Unquestioned belief in group’s morality
• Stereotyped views of adversaries (too evil to
negotiate with, too stupid to be a threat)
• Pressure directing at any dissenting group member
• A shared illusion of unanimity
• Self censorship of deviations from group consensus
• Self-appointed “mind guards” protect group from
information that might challenge the complacency
Group Polarization
[Moskovici & Zavaloni, 1969]
• The “risky shift” phenomenon [Stoner, 1961]:
Individuals tend to take more risks after a group
discussion
• Can be also a “cautious shift,” and in any judgment
• Possible explanations:
– The extreme majority alternative gets more discussion time
– Responsibility is shared among individual members
– Extreme individuals become more extreme when they
discover that their opinion is not as extreme as viewed
– The extreme alternative is valued higher due to group effect
– Groups are risk-neutral while members are risk-averse
Social Loafing
• People do not work as hard in groups as they work
alone (e.g., rope tugging, even when blindfolded)
• Responsibility for the final outcome is diffused
among members of the group
• Multiple examples from reality and research:
–
–
–
–
Reporting a crime viewed by many people in New York
Assisting a child lost on the highway in Italy
Assisting a stranger pick up coins in an elevator
Intervening as a bystander to report a fire, or to assist a
stranger who cries for help in a nearby room
• Presence of others reduces likelihood of intervention
Group Discussion Modes
• Multiple facilitation techniques are potentially applicable
–
–
–
–
Collective: averaging without interaction
Consensus: Face to face discussion until agreement
Dialectic: members discuss biasing factors
Dictator: Discussion leads to selection of representative
(“best”) member
– Delphi: Judgments provided ahead of time and consensus is
established iteratively in several rounds
• The Collective method was the worst, but the Dictator
method was up to three times more accurate in an
experiment involving sales prediction [Davis, 1973]
Group Decision Making Rules
•
•
•
How does a group reach a decision?
Multiple potential methods exist, such as a
simple majority, total agreement, etc.
A crucial difference exists between
1. choosing among two alternative
2. Choosing among three or more alternatives
•
The difference is in the ability
1. to reach non-paradoxical results, such as an
undesirable effect of irrelevant options
2. To avoid potential manipulation by one of the
decision makers
The Condorcet [1785] Paradox
•
•
•
•
1/3 of the group prefers x>y>z
1/3 of the group prefers y>z>x
1/3 of the group prefers z>x>y
Thus:
– an absolute 2/3 majority prefers x to y
– an absolute 2/3 majority prefers y to z
– But: an absolute 2/3 majority prefers z to x
• Inconsistent with a transitivity assumption (!!)
The Borda Scoring Rule
• Each group member ranks all K alternatives,
giving the best K points and he worst 1 point
• Points are summed to determine the decision
• However, the assumption of independence
from irrelevant alternatives (IIA) is violated
• For example, removing 3 inferior alternatives
from a list of 5 alternatives can change the
preference order for the two main alternatives!
Example of Borda IIA Violation
•
Assume 5 individuals and 5 alternatives a,b,c,x,y:
1.
2.
3.
4.
5.
•
•
x>y>a>b>c
y>a>c>b>x
c>x>y>a>b
x>y>b>c>a
y>b>a>x>c
Note: x>y
Note: y>x
Note: x>y
Note: x>y
Note: y>x
Thus, score(y) = 21 > score(x) = 17; y>x by group
But: removing a,b,c leads to:
–
score(x) = 8 > score(y) = 7; x>y by group!
The Importance of the Comparison Order
•
Assume 3 individuals and 3 alternatives x,y,z
1. x>y>z
2. y>z>x
3. z>x>y (or: x>z>y)
•
•
•
If we first compare x to z, z wins and then y wins; if
we first compare x to y, x wins and then z win
The comparison order (e.g., as determined by a
committee head in a parliament) is crucial!
The third individual can change the eventual winner
by manipulating their preferences so that x wins
when compared to z and then wins over y!
The Arrow [1951, 1963]
Impossibility Theorem
• It is impossible to find a group decision rule for
choosing the preferred alternative out of three or
more alternatives, without potentially leading to a
paradoxical result (i.e., more than one chosen
alternative)
• Shows that at least one of four given assumptions,
such as independence of irrelevant alternatives,
cannot be maintained
• Later results show that every reasonable election
method for one candidate out of three or more can be
manipulated by voting against one’s own preferences
Summary:
Group Decision Making
• Advantages:
– Multiple views and types of expertise
– Social facilitation due to directed open discussion
– Brainstorming might lead to creative solutions
• Disadvantages:
– Often fails to equal the best individual solution
– Conformity bias (e.g., the Asch (1951-1956) 3 lines experiments)
– Groupthink (overconfidence, ignorance of facts)
– Polarization effect (e.g., “risky shift” phenomenon)
– Social loafing (pool, elevator experiments)
– In general: No optimal decision rule exists for more than 2 options
• Much depends on how the discussion is managed (e.g., order of
speaking; use of a discussion facilitator; a consensus, dictator or a
Delphi methodology)