1. Lecture 10
Social Networks, Network Structures and Information Systems Part II: Homophily and Social Capital

2. The power of social capital
1 + 1 = 2
Fully connected network:
N people, N(N-1)/2 ties
Connections grow at a much faster rate
(quadratic vs. linear)
1 + 1 > 2?
2 + 2 > 4?
Bridge
6 + 6 > 12?

4. Linking ‘Social Capital’ and the Principle of Homophily
Two important concepts in structural arguments and network outcomes:
Social Capital
Homophily

5. Social “Capital”
Networks as a resource: access to information, goods, services.
Cross-cutting social circles revisited:
The greater the number of intersecting social circles of which a node is a member, the greater the node’s social capital
Race
Education
Age

6. Simmel (1955) and Blau (1984) “Cross-cutting social circles”
Race
Education
Age
Circles can also be other categories: i.e., political affiliations, religions, etc. They are not necessarily well-defined groups.

7. Homophily
People interact more often with people who are “like them” than with people who are dissimilar.
Age, gender, race/ethnicity, education, music
“We are a moving average of our associates.” (Miller McPherson)
Homophily is the principle that a contact between similar people occurs at a
higher rate than among dissimilar people. The pervasive fact of homophily means
that cultural, behavioral, genetic, or material information that flows through networks
will tend to be localized.
Homophily implies that distance in terms of
social characteristics translates into network distance, the number of relationships
through which a piece of information must travel to connect two individuals.

8. Birds of a Feather: Homophily in Social Networks
Two types (Lazarsfeld and Merton 1954)
Status Homophily
Value Homophily
‘Baseline’ and ‘Inbreeding’ homophily
Causes
Structural: Geography, Family, Organizational affiliations
Cognitive: Choosing to interact with similar others
Common norms may bring individuals together with common attributes, and common attributes may lead to common norms
“jackdaw percheth beside jackdaw”
Status homophily: similarity based on informal, formal or ascribed status.
Value homophily: similarity based on values, attitudes and beliefs.

9. Homogeny Vs. Homophily Principle of interaction between individuals
Characteristic (descriptive) of groups

10. Information Flows and Structure
Homophily affects the distribution and flow of information between individuals. It is a central part of understanding…
… diffusion of Innovation
… distribution of cultural forms (music, religion, among others)
… information sharing and the distribution of knowledge through networks

11. Example: Music (Mark 1998)
Music “forms” depend on people for their existence.
Music types carve out niches in different sociodemographic segments of society.
Music preferences are transmitted through network ties, which tend to be homophilous, leading to similar tastes among similar people.

12. From Mark, 1998 “Birds of a Feather Sing Together” Social Forces

13. Homophily and Information Technology
How do strong ties relate to the concept of homophily? Weaker ties?
Is homophily ‘a bug or a feature’?
How might it relate to ‘search’? To diffusion of information and/or innovations?
Leskovec and Horvitz, Worldwide Buzz: Planetary-Scale Views on an Instant-Messaging Network
ftp://ftp.research.microsoft.com/pub/tr/TR pdf

14. What can we learn from studies like these?
The processes do not appear to change so much over time (effects of weak ties, homophily), but systems like the Internet—the technology– provides opportunities to connect on a wider range of dimensions.
The structure of a given network can have significant effects on outcomes at the (a) individual and (b) aggregate level.
Individual level: Capacity to get/receive assistance, advice, help, resources.
Aggregate level: Regardless of individual efforts, the network structure in which a group of individuals are embedded can impact success/failure of some outcome(s).