L'influence des Liens Sociaux sur la Santé

Thomas W. Valente, PhD

November 28, 2012Montréal, Quebec

Professor, Institute for Prevention ResearchPreventive Medicine, Keck School of Medicine

University of Southern Californiatvalente@usc.edu

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Acknowledgements

• Thanks:– Yun Jen

• National Institutes of Health (NIH)– NIDA/OBSSR

• Center for Prevention Implementation Methodology

• University of Miami

– NIAAA RC1AA019239NIAAA RC1AA019239• Social Networks and Networking ...

– NCI: R0110866440• Social Networks and Health

• Kar-Hai Chu, PhD, for animations

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What is a network?

• A set of relations connecting unitsF i d hi ( i h l li )– Friendships (e.g., in schools or onlin)

– Trading relations among countries

– Exchanges between firms

– Collaboration & cooperation among organizations.

Sample Social Network

Bob Sue

Ted

Sam

Liz

AmyDistance Bob to Sam=2Distance Sam to Bob=4

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Why Study networks?

• Spread Disease

• Spread Behaviors

• Spread new ideas

• Important Planning and Policy

• Understanding Markets and Diffusion

And so onAnd so on …

Relationships of 10th graders

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Discussion Network for SF MDs

After School Program Directors

1

14

5

410

12

11

15

13

16

55

57

59

KK1

Y1 

KK- Kids

YMCA

14

3

1920

23

64

72

6

10

789

2

17

24

26

27

30

3241 51

48

9133

36

40

5354 4544

47

50

5856

65

77KK2 

28

3029

3739

40

31

4635

38

42

43 95

52

34

88

49

60 6162

6380

89

118

Y2 

Y3 

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Network Properties (1)

• Homophily (like sorts with like)

Network Properties (2)

• Transitive (friends of friends become friends))

Bob

John Ken John

Bob

KenJohn Ken John Ken

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Network Properties (3)

• Scale Free: Centralized (e.g., some people are popular)p p )

Network Properties (4)

• Small World: Local clusters connected by bridgesy g

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Diffusion/contagion

• Today we’ll focus on the importance of networks for understanding how to usenetworks for understanding how to use networks to understand and change behavior.

Network Diffusion 

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Network Exposure/Peer Influence

=non-user =user

A B

Person A has only 1 user in his/her network whereas person has 4 and so much more likely to adopt.

Evidence for network effects

• Adolescents with smoking friends are more likely to smoke;more likely to smoke;

• Physicians use the same therapies their colleagues use;

• Women in developing countries use the same contraception as their friends; and

• Smokers quit when their network quits.

• …

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Networks Can Also be Organizations or Countries

• Inter‐firm and market competition;

• Inter‐organizational collaboration; and

• Inter‐state or inter‐country diffusion.

3 Treaties Diffused 2001‐2010

1

FCTC Corrupt Pollute

0,4

0,5

0,6

0,7

0,8

0,9

0

0,1

0,2

0,3

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Diffusion at Policy LevelDiffusion at Policy LevelCountry Ratifications of FCTCCountry Ratifications of FCTC

100

nt Italy

40

60

80

lati

ve

Ad

op

tio

n P

erc

e

Lebanon

Iceland

19

0

20

20032003

20042004

20042005

20052005

20062006

20062007

20072007

20082008

2008

Time

Cu

mu

l

Norway

Co-membership on GlobalinkEarliest (15.5%) Non-Ratifiers (17.1%)

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FCTC Diffusion

To accelerate diffusion:Use Networks to Identify Opinion Leaders

• OL interventions are the most typical network interventionnetwork intervention

• Easy to measure

• Intuitively appealing

• Proven effectiveness

• Over 20 studies using network data to• Over 20 studies using network data to identify OLs and hundreds of others using other OL identification techniques

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Central People are Potential Opinion LeadersCentral People are Potential Opinion Leaders

Central Members

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Simulation w/ 3 Initial Adopter Conditions

40

60

80

100

ent

Ad

op

ters

Opinion Leaders

Random

Marginals

0

20

1 2 3 4 5 6 7 8 9 10

Time

Per

ce

Marginals

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Role of Leaders / Influentials in the Adoption Process

6. ConfirmationOngoing experience confirms decision to

adopt May move to be an advocateadopt. May move to be an advocate

3. Persuasion / EvaluationTalks to others to gather information and

Mentally considers use

4. Decision to TryConvinced to trial to see if

it will be useful

5. AdoptionCompares personal experience with

expectations and considers future use

Regional

Local OLs

Peers

Six Steps in the

Adoption Process

1. AwarenessFirst learns of new product,

but unaware of benefits

2. InterestSearches for information about the new

product. Talks to trusted friends & experts

Mentally considers use

National Opinion Leaders

Regional

Opinion Leaders

Network Effects

Steps to Opinion Leader InterventionsSteps to Opinion Leader Interventions

1) Collect/obtain network data

2) Identify opinion leaders

3) Recruit them as champions

4) Convert them (if need be)

5) Assist them in their behavior5) Assist them in their behavior change promotions

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Network Interventions

• Network interventions are any change program designed to improve p g g porganizational performance, promotion campaigns, and/or social mobilization that uses network data to:– Select change agents– Define groupsg p– Affect network structure – Assist behavior change program

implementation

Principle 1: Program Goals Matter

• In some cases want to increase cohesion in others increase fragmentationin others increase fragmentation

• Increase/decrease centralization

• E.g., slowing spread of STDs requires different strategy than accelerating adoption of office automation

• Network Interventions Are not Agnostic to Content.

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Principle 2: Theory

• The type of change desired will be guided by theory (Behavior v Attitude)guided by theory (Behavior v Attitude)

• Understanding motivations for and barriers against behavior change is critical.

• A well-articulated theory of the behavior is often critical for successful interventions.

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Principle 3: Learn As Well As Induce

• The interventionist should use network methodology to learn from the communitymethodology to learn from the community as much as try to influence it.

• Programs which meet the needs of their audiences are better received than those designed asymmetrically.

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Network Interventions

Strategy Tactic Operationalization

Identification LeadersBridgesKey PlayersPeripheralsLow Thresholds

Degree, Closeness, etc.Mediators,  BridgesPositive, Negative

Proportions, Counts

Segmentation GroupsPositions

Components, CliquesStructural Equivalence,  Hierarchies

Induction WOMSnowballMatching

Random ExcitationRDS, OutreachLeaders 1st, Groups 1st

Alteration (Manipulation)

Deleting/Adding NodesDeleting/Adding LinksRewiring

VitalityOn Cohesion, OthersOn Network, On Behavior

Graphical Displays of Intervention Choices

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Graphical Displays of Intervention Choices

Selecting a NI

• Availability and type of data

T f k– Types of networks

– Existing network structure

• Behavioral characteristics

– Existing prevalence

– Perceived characteristics such as cultural compatibility; cost; trialability; etc.

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Linking Theory to Intervention Strategy

• There are several theoretical mechanisms that drive contagion and behavior changedrive contagion and behavior change

• Evidence for a particular mechanisms suggests choice of intervention strategy or tactic

Influence Mechanisms Aligned with Interv. Choices

Mechanism Tactic

PowerConflict

LeadersBridges

CohesionIsolationThresholds

gKey PlayersPeripheralsLow Thresholds

Group IdentificationStructural Equivalence

GroupsPositions

Information diffusion WOMInformation diffusionHard to reach populationsClosureHomophily

WOMSnowballOutreachMatching

AttributesStructureStructure!!

Deleting/Adding NodesDeleting/Adding LinksRewiring

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Conclusions Conclusions 

• Network theories and methods can be used t d t d ti ti f d to understand motivations for and processes of human behavior change.

• Network interventions have the promise of improving outcomes (health, organizational performance, etc.); and

• Test theoretically interesting network theories.

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More reading and information:www-hsc.usc.edu/~tvalente/

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