group decision making sf

8/8/2019 Group Decision Making SF

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Group Decision Makingand Voting

Simon French

[email protected]



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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



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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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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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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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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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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



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The challenge for TED is

not so much

to develop new decision analyticmethods

but

to address issues of communicationand of explaining our existing methods

to a wider and much more dispersedaudience

group decision making sf

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