Social Network Analysis
Some of the key concepts of Network Metrics come from the
field of Social Network Analysis, or SNA. SNA provides a set of
methodologies and formulas for calculating a variety of criteria
that map and measure the links between things. Using SNA, you
can get answers to questions like:
- How highly connected is an entity within a network?
- What is an entity's overall importance in a network?
- How central is an entity within a network?
- How does information flow within a network?
SNA provides a rich set of metrics, many of which are used in
the Sentinel Visualizer Network Metrics functionality.
Degree Centrality
Degree centrality is simply the number of direct
relationships that an entity has. An entity with high degree
centrality:
-
Is generally an active player in the
network.
-
Is often a connector or hub in the network.
-
Is not necessarily the most connected entity
in the network (an entity may have a large number of
relationships, the majority of which point to low-level
entities).
-
May be in an advantaged position in the
network.
-
May have alternative avenues to satisfy
organizational needs, and consequently may be less dependent
on other individuals.
-
Can often be identified as third parties or
deal makers.
In our example network diagram, Alice has the
highest degree centrality, which means that she is quite active
in the network. However, she is not necessarily the most
powerful person because she is only directly connected within
one degree to people in her clique—she has to go through Rafael
to get to other cliques.
Betweenness Centrality
-
Betweenness centrality identifies an
entity's position within a network in terms of its ability
to make connections to other pairs or groups in a network.
An entity with a high betweenness centrality generally:
-
Holds a favored or powerful position in the
network.
-
Represents a single point of failure—take
the single betweenness spanner out of a network and you
sever ties between cliques
-
Has a greater amount of influence over what
happens in a network.
In this example, Rafael has the highest
betweenness because he is between Alice and Aldo, who are
between other entities. Alice and Aldo have a slightly lower
betweenness because they are essentially only between their own
cliques. So although Alice has a higher degree centrality,
Rafael has more importance in the network in certain respects.
Closeness
Closeness centrality measures how quickly an entity can
access more entities in a network. An entity with a high
closeness centrality generally:
- Has quick access to other entities in a network.
- Has a short path to other entities.
- Is close to other entities.
- Has high visibility as to what is happening in the network.
As with the betweenness example, Rafael has the highest
closeness centrality because he can reach more entities through
shorter paths. As such, Rafael's placement allows him to connect
to entities in his own clique, and to entities that span
cliques.
Note: If the network contains any entities that are
un-linked (i.e. not linked to any other entities), the Closeness
value for all entities in the network is 0. This is due to
formulas and algorithms established in Social Network Analysis.
Eigenvalue
Eigenvalue measures how close an entity is to other highly
close entities within a network. In other words, Eigenvalue
identifies the most central entities in terms of the global or
overall makeup of the network. A high Eigenvalue generally:
- Indicates an actor that is more central to the main
pattern of distances among all entities.
- Is a reasonable measure of one aspect of centrality in
terms of positional advantage.
In this example, we can see that Alice and Rafael are
closer to other highly close entities in the network. Bob
and Frederica are also highly close, but to a lesser value.
Hub and Authority
Entities that many other entities point to are called
Authorities. In Sentinel Visualizer, relationships are
directional—they point from one entity to another. If an
entity has a high number of relationships pointing to it, it
has a high authority value, and generally:
- Is a knowledge or organizational authority within a
domain.
- Acts as definitive source of information.
Hubs are entities that point to a relatively large
number of authorities. They are essentially the mutually
reinforcing analogues to authorities. Authorities point
to high hubs. Hubs point to high authorities. You cannot
have one without the other. |
