publishing network researchanalytictech.com/networks/basic concepts 2002.pdf · 2015. 10. 12. ·...
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Integration. Nick Athanassiou and friends4:30-5:00
Sharing Network Research inProgress. Roundtables
Analyzing Network DataSteve & David
3:15-4:30BREAK3:00-3:15
Publishing Network Research.Panel discussion.
Analyzing Network Data.Steve Borgatti
2:15-3:00
Data Collection. David Krackhardt1:30-2:15LUNCH12:15-1:30
Designing Network Research. Julie Hite & Dan Brass11:00-12:15MINI-BREAK10:53:21-11:00
Survey of Network Research. Dan Brass9:37-10:53:20MINI-BREAK9:30-9:37Basic Concepts. Steve Borgatti8:15-9:30Welcome. Nick Athanassiou (organizer)8:00-8:15Registration & breakfast social7:30-8:00
SCHEDULETIME
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BasicSocial Network
Concepts
Handouts available atwww.analytictech.com/aomnetwork
AoM PDW @ DenverAugust, 2002
Steve Borgatti, Boston Collegewww.analytictech.com/borgatti
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What is a Network?
• A set of dyadic ties, all of the same type,among a set of actors
• Actors can be persons, organizations …• A tie is an instance of a social relation
Bill
Bob
Betsy
Bonnie
Betty
Biff
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Relations Among Persons
• Kinship– mother of, wife of
• Other role-based– boss of, teacher of– friend of
• Cognitive/perceptual– knows– aware of what they know
• Affective– likes, trusts
• Interactions– give advice, talks to,
fights with– sex / drugs with
• Affiliations– belong to same clubs– is physically near
Note: Content matters!Each relation yields a different structure & has different effects
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Simple Answers
Data drawn from Cross, Borgatti & Parker 2001.
Recent acquisition
Older acquisitions
Original company
HR Deptof LargeHealth CareOrganization
Who you ask for answers to straightforward questions.
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Problem Reformulation
Recent acquisition
Older acquisitions
Original company
Data drawn from Cross, Borgatti & Parker 2001.
Who you see to help you think through issues
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Marriage Ties AmongFlorentine Families
Data compiled by John Padgett
During Renaissancetimes
Exampleof a Network
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Relations Among Organizations
• As corporate entities– Buy from / sell to, leases
to, outsources to– Owns shares of,
subsidiary of– Joint ventures, cooperate
sales agreements,alliances
– Regulates
• Via their members– Personnel flows– Interlocking directorates– Personal friendships– Co-memberships
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BPSCAR
CM
ENT
GDO
HCM
HR
IM
MC
MED
MH
MSRMOC
OM
OMT
ODC
OB
OCIS
ONE
PN
RM
SIM
TIM
AoM Co-Membership
> 27% overlap
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Internet Alliances
AOLMicrosoft
Yahoo
AT&T
Exampleof a Network
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Kinds of Network Data
+**2-mode
++++++++1-modeEgoComplete
Patient
PDRMerck
manual
Web MDDr. JonesBill
MomJane
Bill
Bob
Betsy
Bonnie
Betty
Biff
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Data collected by Cross
1-mode complete network
Informationflow withinvirtual group
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1-mode ego networkCarter Administration meetings
Data courtesy of Michael LinkYear 1 Year 4
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Ego Network Analysis
• Combine the perspective of network analysiswith the data of mainstream social science
• No computer programs available
NetworkAnalysis
MainstreamSocial Science
EgoNetworks
perspectivedata
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2-mode Ego Network
Patient
PDRMerck
manual
Web MDDr. JonesBill
MomJane
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2-mode complete network
Data compiled from newspaper societypages by Davis, Gardner & Gardner
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The Network Perspective
• Relations vs. Attributes– Individual characteristics only half the story– People influence each other, ideas & materials flow– Predicting adoption of innovation– Interdependence vs atomistic essentialism
• Structure vs. Composition– It’s not just the elements of a system, but how
they are put together– non-reductionist, holistic, systemic
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The Network Perspective
• Emergence vs. Design– groups (e.g., communities vs. departments)– roles
• Structuralism vs individualism– structure -> group performance– position -> opportunities & constraints– Faith that social capital trumps human capital– more research on consequences of network structure &
position than causes– Preference for direction of causality
• position -> personality, not the reverse
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Graph Theoretic Concepts
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Directed vs undirected ties
• Undirected relations– Attended meeting with– Communicates daily with
• Directed relations– Lent money to
• Logically vs empirically directed ties– Empirically, even un-
directed relations canbe non-symmetric due tomeasurement error Bob
Betsy
Bonnie
Betty
Biff
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Strength of Tie
• We can attach values to ties,representing quantitative attributes– Strength of relationship– Information capacity of tie– Rates of flow or traffic across tie– Distances between nodes– Probabilities of passing on information– Frequency of interaction
Bob
Betsy
83
Jane
61
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Adjacency MatricesFriendship
Jim Jill Jen JoeJim - 1 0 1Jill 1 - 1 0Jen 0 1 - 1Joe 1 0 1 -
ProximityJim Jill Jen Joe
Jim - 3 9 2Jill 3 - 1 15Jen 9 1 - 3Joe 2 15 3 -
Jim
Jill
Jen
Joe
3
2
9
1
153
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Data FormatsDl n = 5Format = fullmatrixLabels embeddedData:
Dl n = 5Format = edgelistLabels embeddedData:Billy jillBilly john 6.3Dick janeJim bob 2.5
Dl n = 5Format = nodelistLabels embeddedData:Billy jill john jim janeJill billy bob berthaDick janeJim bob billy brenda
(No values possible) (Values optional – assigned 1 if omitted)
0101mary1000jill0101john0010billy
maryjilljohnbilly
(Values optional)
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1
2
3
4 5
6
7
89
10
11
12
Walks, Trails, Paths
• Path: can’t repeat node– 1-2-3-4-5-6-7-8– Not 7-1-2-3-7-4
• Trail: can’t repeat line– 1-2-3-1-7-8– Not 7-1-2-7-1-4
• Walk: unrestricted– 1-2-3-1-2-7-1-7-1
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Length & Distance
• Length of a path isnumber of links
• Distance between twonodes is length ofshortest path (akageodesic)
1
2
3
4 5
6
7
89
10
11
12
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Geodesic Distance Matrix
0124334g
1013223f
2102112e
4320123d
3211012c
3212101b
4323210a
gfedcba
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Components
• Maximal sets of nodes in which every nodecan reach every other by some path (nomatter how long)
• A connected graph has just one component
Relations form different networks. Components don’t.
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A network with 4 components
Recent acquisition
Older acquisitions
Original company
Data drawn from Cross, Borgatti & Parker 2001.
Who you go to so that you can say ‘I ran it by ____, and she says ...’
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Independent Paths
• A set of paths is node-independent if they share nonodes (except beginning and end)– They are line-independent if they share no lines
ST
• 2 node-independent paths from S to T• 3 line-independent paths from S to T
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Cutpoints
• Nodes which, if deleted, would disconnect net
Bill
Bob
Betsy
Bonnie
Betty
Biff
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a
b
c
d
e
f
g
h i j
k
l
m
n
o
p
q
r
s
Bridge
• A tie that, if removed, would disconnect net
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Local Bridge of Degree K
• A tie that connects nodes that wouldotherwise be at least k steps apart
AB
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Granovetter’s SWT Theory
• Strong ties create transitivity– Two nodes connected by a strong tie will have
mutual acquaintances (ties to same 3rd parties)• Ties that are part of transitive triples cannot
be bridges or local bridges• Therefore, only weak ties can be bridges
– Hence the value of weak ties• Strong ties embedded in tight homophilous
clusters, weak ties connect to diversity– Weak ties a source of novel information
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Granovetter Transitivity
A
B
C
D
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Network Cohesion
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Connectivity
• Line connectivity � isthe minimum number oflines that must beremoved to disconnectnetwork
• Node connectivity κ isminimum number ofnodes that must beremoved to disconnectnetwork
ST
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Fragmentation
• Proportion of pairs of nodes that areunreachable from each other
)1(
)1(1
�
�
��
�
nn
ssF k
kk
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Density
• Number of ties, expressed as percentage of the number ofordered/unordered pairs
Low Density (25%)Avg. Dist. = 2.27
High Density (39%)Avg. Dist. = 1.76
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Help With the Rice Harvest
Data from Entwistle et al
Village 1
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Help With the Rice Harvest
Whichvillageis morelikely tosurvive?
Village 2Data from Entwistle et al
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Average Distance
• Average distance between all pairs of nodes
Core/Peripheryc/p fit = 0.97, avg. dist. = 1.9
Clique structurec/p fit = 0.33, avg. dist. = 2.4
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Centralization
• Degree to which network revolves around asingle node
Carter admin.Year 1
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Transitivity
• Proportion of triples with 3 ties as aproportion of triples with 2 or more ties– Aka the clustering coefficient
T
A
B C
DE
{C,T,E} is atransitive triple,but {B,C,D} is not
cc = 2/6 = 33%
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Core/Periphery Structures
• Does the network consist of asingle group (a core) togetherwith hangers-on (a peri-phery), or
• are there multiple sub-groups, each with their ownperipheries?
C/P struct.
Cliquestruct.
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Subgroup Cohesion
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Graph-Theoretic Concepts
• Structural definitions of groups– Clique– N-clique, n-clan, n-club– K-core, K-plexes– Ls-set, Lambda sets– Factions
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Clique
• Maximal set of actors in which every actors isconnected to every other
• Properties– Maximum density (1.0)– Minimum distances (avg = 1)– overlapping
a bc
d
e fa b
c
d
e fa b
c
d
e f
{c,d,e} & {b,c,d} are cliques
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N-Clique
• A set of nodes that are within distance n ofeach other
• Relaxes distanceaspect of cliqueconcept– 1-clique is just a
cliquea
b c
d
ef
{a,b,c,e,f} is a 2-clique
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K-Plex
• A set of n nodes in which every node has a tieto at least n-k others in the set– In a 1-plex, every node is connected to all but one
others in the set – i.e., is a clique
a b
c
deIs {a,b,c,d,e} a 2-plex?
{a,b,d,e} is a 2-plex:each node tied to 4-2others in set.
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Factions
• A set of mutually exclusivegroups of actors such thatdensity of ties within groupis greater than density ofties between groups
-010010g
1-10000f
11-0000e
000-101d
0011-10c
10011-1b
010011-a
gfedcba
Density within group: 14/18 = .78Density between groups: 4/24 = .17
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Individual Cohesion
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Centrality
• Path-based– Degree– Closeness– Betweenness– Flow betweenness– Redundancy/constraint
• Walk-based– Eigenvector– Bonacich Power– Katz– Hubbell
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Degree Centrality
• The number of nodes adjacent to given node
HighestDegreeCentrality
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Closeness Centrality
• Sum of geodesic distances to all other nodes• Inverse measure of centrality
“Highest”ClosenessCentrality
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HighestBetweennessCentrality
Betweenness Centrality
• Loosely: number of times that a node liesalong the shortest path between two others
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HighesteigenvectorCentrality
Eigenvector Centrality
• Iterative version of degree centrality: anode’s centrality is proportional to the sum ofcentralities of those it has ties to
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Structural Holes
• “cheap” betweenness
Ego Ego
Few structural holes Many structural holes: - power, info, freedom
structuralhole
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Structural Holes
Slide from Ron Burt
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Entrepreneurial Network
– sparse, flat structure– independent relations,
sustained by manager– structural holes, low
redundancy provides info &control benefits
– associated with successfulmanagers
manager
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Support Network
– dense, flat structure– interdependent relations
sustained by each other formanager
– few holes, high redundancycreates social support
– associated with unsuccessfulmanagers
manager
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Structural Similarity
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Network Neighborhoods
• An actor’s neighborhood is the set of actorsthey are connected to
• For directed networks:– In-neighborhood
• Actors sending ties tofocal actor
– Out-neighborhood• Set of actors receiving
ties from focal actor
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Structural Equivalence
• Actors are structurally equivalent to theextent they have the same in-neighborhoodsand out-neighborhoods
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Structurally equivalent nodes are colored the same
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Structural Equivalence
• Structurally indistinguishable– Same degree, centrality, belong to same number of
cliques, etc.– Only the label on the node can distinguish it from
those equiv to it.– Perfectly substitutable: same contacts, resources
• Face the same social environment– Similar forces affecting them
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Structural Equivalence
• Captures notions like niche• Location or position
– You are your friends
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BlockModeling
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Regular Equivalence
• B and D are structurally equivalent but what Band G?– E on left has mirror-image counterpart F
• Structural equivalence is to equality whatregular equivalence is analogy
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Regular Equivalence
• Two actors are regularly equivalent if theyare connected to equivalent others– Not necessarily same others– Not necessarily in same quantity
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Technical Definition
– For any third party i that u� i, there exists an actor jthat v � j and j is regularlyequivalent to i
– For any third party i that i� u, there exists an actor jthat j � v and j is regularlyequivalent to i
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• If two actors u and v are regularlyequivalent, this implies that
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Regular Equivalence
• Captures notion of role counterpart– Two doctors equivalent because they have same
kinds of relations with same kinds of others, suchgiving advice to patients, giving orders to nurses,receiving products from vendors, etc.
– Works when when roles are emergent – unnamed• Captures position in hierarchies well
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Blockmodel View
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Hierarchical Positiona b
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Categorizing SN Concepts
CohesionDensity;avg dist;
centralization
Wholenetwork
Structural ®ular equiv
classesSimilarity
CentralityDegree;
closeness;betweenness;Struct holes
GroupsCliques;n-clique;k-plex
Connection
IndividualactorsSubsets
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Social Capital
• Group level concept: cohesion– pattern of ties among members of a group confers
competitive advantage• immigrant groups, organizations, countries
• Individual level concept: centrality– benefits of being well connected
• material aid• information (broadly defined)• fun, companionship, emotional support, love ...
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To Learn More ...
• Workshop web site:– www.analytictech.com/aomnetwork
• INSNA web site:– www.heinz.cmu.edu/project/INSNA
• Contact me via email:– [email protected]
• Papers on-line:– www.analytictech.com/borgatti/paperson.htm