Group Decision Making SF
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Transcript of Group Decision Making SF
8/8/2019 Group Decision Making SF
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Group Decision Makingand Voting
Simon French
8/8/2019 Group Decision Making SF
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What is decision support?
Normative models of decision how we should make decisions rationally
Descriptive models of decision how we do make decisions, often irrationally
Empirically what we do and what we shouldare not the same
Groups are composed of real people so must help irrational people but should work if group members are rational
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Prescriptive Decision Analysis
Normative Decision
Theories
provide models of howpeople should make
inferences anddecisions
Descriptive Decision
Theories
provide models of howpeople do make
inferences anddecisions
Prescriptive Analyses
seek to guide decision makers towards theideals encoded by normative theorieswithin the context of a real, often ill-defined
problem, mindful of their cognitivecharacteristics
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Prescriptive decision analysis andsupport
helps the decision makers understandthe issues better and the balance
between their beliefs and preferences
through that understanding they not the models and analyses make the
decision
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A couple of Questions
Hands up!
Who believes in democracy?
Who believes in fairies?
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Group Decision Making
Most decisions are made in groups
In democracy, society is the group
so key questions for e-democracy are:
What do we mean by group decisionmaking?
Does group decision making exist?
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Group intransitivity
Individual 1: a H1 b H1 c.
Individual 2: b H2 c H2 a.
Individual 3: c H3 a H3 b.
Simple M jority Vote
H g b, si ce o t of prefer a to b.
b H g c, si ce o t of prefer b to c.
cH g a, si ce o t of prefer c to a.
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Agenda Rigging
Individual 1: a H1 b H1 c.
Individual 2: b H2 c H2 a.
Individual 3: c H3 a H3 b.
a
b
}p a
c}p
c
b
c
}p b
a}pa
but
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Arrows Theorem
No constitution (voting system) satisfies:
Weak ordering (complete, transitive)
Non TrivialityUniversal domain
Independence of the irrelevant alternative (IIA)
Pareto Principle
No Dictatorship
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Sketch Proof (1)
Define a decisive subset V of the group for a over b by:when V unanimously prefers a to b, the group does.
Pareto principle implies the group is decisive for all aover b
Suppose that V is a minimal decisive subset, i.e. is the
smallest such subset for any pair a and b
Suppose it is decisive for a over b.
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a bc3rd
ca b2nd
bca 1st
UW{j}
< V >
Sketch Proof (2)Suppose #{ V} > 2.
Suppose group is bigger tha n 3 a nd ha s > 3 a lterna tives (Non-trivia lity, Universa lity)
Ca n use IIA to consider triplets of a lterna tives without considering rest of possibilities.
V decisive, group prefers a to b
W not decisive, group ca nnot prefer cto b: so b a t lea st a s good a s c forgroup
Tra nsitivity: group prefers a to c.
So {j} is decisive for a over c
Contra diction => #{ V} = 1
Simila r a rguments show j, the single member of V, isdecisive for a ll a lterna tive pa irs a dict a tor!
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Attempts to avoid Arrows result
Since 1951 there have been many attempts
to find a flaw in Arrows reasoning
to argue that it is irrelevant to democracy
Essentially all have failed.
In fact, each of the assumptions may bedropped and a version of his Theorem stillholds.
In practice, it wont happen
But it does RSS nominating committee.
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Worse still
Might someone be dishonest?
Gibbard-Satterthwaite Theorem:For > 3 alternatives, no voting systemsatisfies:
universal domain
non-dictatorship non manipulability
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Strength of Preference
Some suggest that the problem is that thegroup only give rankings
So if they indicated their strength of
preference all would be solved so who likes apples and oranges?
While an individual may compare his or herstrength of preference
All preferences are in a single mindinterpersonal comparisons are meaningless or pretty nearly so.
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Voting
Many different methods of voting
simple ma jority voting
single transferable vote
multiple transferable votes
Borda count
approval voting
all fail one or more of Arrows axioms in somecircumstances
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A couple of Questions
Hands up!
Who believes in democracy?
Who believes in fairies?
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So beware
Many DSSs have inbuilt votingprocedures
Given Arrows result, can such DSSs make sense
support the growth of understanding?
e-democratic systems face the same
difficulty.In fact, all democratic systems do
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So take another direction
For small to moderate size groups
Game theory studies of the essence of conflict
not really a normative theory leading to aprescriptive approach
Negotiation and Bargaining
coming up in the next sessionSocial Process Perspective
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Group decision making is a socialprocess
We need to:
facilitate that process:
foster effective communication between the members;
explore the issues in a creative, effective manner; reduce unproductive tensions and disagreements;
build a shared understanding;
build a commitment to implement the selected course of action.
support each members own thought processes, judgements and decision making
and help them towards a Pareto optimal solution
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Group DSS
Same time Different time
Sameplace
face to face meetings
copyboards
PC pro jection toolsGDSS rooms
Collaboration tools
Voicemail and email
discussion groupscirculation of decision analysisfiles
Collaboration
webspaces, e.g.Lotus Quickplace
Different place
Split-site meetings
Tele/video-
conferencingNet meetings
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Group Decision Support Rooms
Flip-charts,
whiteboar s,a projectio
scree s
s pport
team a
recor er
gro p of
ecisio
makers
facilitator
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Group Decision Support Rooms
Flip-charts,
whiteboar s,
a projectio
scree s
s pport
team a
recor er
gro p of
ecisio
makers
facilitator
8/8/2019 Group Decision Making SF
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23
Small groups are not societies!
Small groups form usually because of common interests, goals and culture.
So can tailor and present decisionanalysis assuming that they have asomewhat similar perceptions and
cultures
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Society is disparate
Very few common goals and ob jectives
Many different perceptions
Greatly differing levels of ability.
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The Bayesian Paradigm:From Individual to Society (1)
In the beginning was theindividual
and ever more shall be so?
Savage, De Finetti,
Axiomatics of individualrational belief, preference,choice
Thinking internal to DM
No communication
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The Bayesian Paradigm:From Individual to Society (2)
Decision Analysis Single DM
Analyst helps DM think,
introspect, analyse DM communicates with
analyst to clarify ownthinking
DM owns decision;
analyst loyal to DM Psychotherapy
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The Bayesian Paradigm:From Individual to Society (3)
But decisions are usuallyowned by groups search for theory of
rational group decision social choice; voting
game theory
Arrows impossibility result
Fruitless: cannot treat agroup as a rational entity
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The Bayesian Paradigm:From Individual to Society (4)
Treat groups as social processes
translating individual decisions
which way to vote
into implemented action
Analyst becomes facilitator
Loyal to group or to leader?
Bayesian paradigm helps
individual thinking and analysis
group communication
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The Bayesian Paradigm:From Individual to Society (5)
Now we face taking the paradigminto substantive edemocracy
Balance may move from analysis
towards communication groups are distributed in space and
time
groups have fewer
common interests common languages
loyalty of facilitator/analyst if there are any much more unclear