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Homophily (from Ancient Greek: homoû, 'together' + philíē, 'friendship, love') is the tendency of individuals to associate and bond with similar others, as in the proverb "birds of a feather flock together." The presence of homophily has been discovered in a vast array of network studies: over 100 studies have observed homophily in some form or another, and they establish that similarity is associated with connection. The categories on which homophily occurs include age, gender, class, and organizational role.
The opposite of homophily is heterophily or intermingling. Individuals in homophilic relationships share common characteristics (beliefs, values, education, etc.) that make communication and relationship formation easier. Homophily between mated pairs in animals has been extensively studied in the field of evolutionary biology, where it is known as assortative mating. Homophily between mated pairs is common within natural animal mating populations.
Homophily has a variety of consequences for social and economic outcomes.
Types and dimensions
Baseline vs. inbreeding
To test the relevance of homophily, researchers have distinguished between two types:
- Baseline homophily: simply the amount of homophily that would be expected by chance given an existing uneven distribution of people with varying characteristics; and
- Inbreeding homophily: the amount of homophily over and above this expected value, typically due to personal preferences and choices.
Status vs. value
In their original formulation of homophily, Paul Lazarsfeld and Robert K. Merton (1954) distinguished between status homophily and value homophily, find that individuals with similar social status characteristics are more likely to associate with each other than by chance:
- Status homophily: includes both ascribed characteristics (e.g. race, ethnicity, sex, and age) and acquired characteristics (e.g., religion and education).
- Value homophily: involves association with others who think in similar ways, regardless of differences in status characteristics.
Dimensions
Race and ethnicity
Social networks in the United States today are strongly divided by race and ethnicity, which account for the greatest proportion of inbreeding homophily (though classification by these criteria can be problematic in sociology due to fuzzy boundaries and different definitions of race).
Smaller groups have lower diversity simply due to the number of members. This tends to give racial and ethnic minority groups a higher baseline homophily. Race and ethnicity also correlates with educational attainment and occupation, which further increase baseline homophily.
Sex and gender
In regard to sex and gender, baseline homophily of networks is relatively low compared to race and ethnicity. Men and women frequently live together, and are both large and equally-sized populations. Most sex homophily is of the inbreeding type. Especially in schools, students tend to have a high gender homophily.
Age
Most age homophily is of the baseline type. An interesting pattern of inbreeding age homophily for groups of different ages was found by Marsden (1988). It indicated a strong relationship between someone's age and the social distance to other people with regard to confiding in someone. For example, the larger age gap someone had, the smaller chances that they were confided by others with lower ages to "discuss important matters."
Religion
Homophily based on religion is due to both baseline and inbreeding homophily.
Education, occupation and social class
Family of birth accounts for considerable baseline homophily with respect to education, occupation, and social class.
Interests
Homophily occurs within groups of people that have similar interests as well. We enjoy interacting more with individuals who share similarities with us, so we tend to actively seek out these connections. Additionally, as more users begin to rely on the Internet to find like minded communities for themselves, many examples of niches within social media sites have begun appearing to account for this need. This response has led to the popularity of sites like Reddit in the 2010s, advertising itself as a "home to thousands of communities...and authentic human interaction."
Social media
As social networks are largely divided by race, social-networking websites like Facebook also foster homophilic atmospheres. When a Facebook user 'likes' or interacts with an article or post of a certain ideology, Facebook continues to show that user posts of that similar ideology (which Facebook believes they will be drawn to). In a research article, McPherson, Smith-Lovin, and Cook (2003) write that homogeneous personal networks result in limited "social worlds in a way that has powerful implications for the information they receive, the attitudes they form, and the interactions they experience." This homophily can foster divides and echo chambers on social networking sites, where people of similar ideologies only interact with each other.
Causes and effects
Causes
Geography: Baseline homophily often arises when the people who are located nearby also have similar characteristics. People are more likely to have contact with those who are geographically closer than those who are distant. Technology such as the telephone, e-mail, and social networks have reduced but not eliminated this effect.
Family ties: Family relationships often produce relatively close, frequent contact among those who are at great geographic distance. These ties tend to decay slowly, but can be dramatically restructured when new marriages occur.
Organizations: School, work, and volunteer activities provide the great majority of non-family ties. Many friendships, confiding relations, and social support ties are formed within voluntary groups. The social homogeneity of most organizations creates a strong baseline homophily in networks that are formed there.
Isomorphic sources: The connections between people who occupy equivalent roles will induce homophily in the system of network ties. This is common in three domains: workplace (e.g., all heads of HR departments will tend to associate with other HR heads), family (e.g., mothers tend to associate with other mothers), and informal networks.
Cognitive processes: People who have demographic similarity tend to own shared knowledge, and therefore they have a greater ease of communication and share cultural tastes, which can also generate homophily.
Effects
According to one study, perception of interpersonal similarity improves coordination and increase the expected payoff of interactions, above and beyond the effect of merely "liking others." Another study claims that homophily produces tolerance and cooperation in social spaces. However, homophilic patterns can also restrict access to information or inclusion for minorities.
Nowadays, the restrictive patterns of homophily can be widely seen within social media. This selectiveness within social media networks can be traced back to the origins of Facebook and the transition of users from MySpace to Facebook in the early 2000’s. One study of this shift in a network’s user base from danah boyd (2011) found that this perception of homophily impacted many individuals' preference of one site over another. Most users chose to be more active on the site their friends were on. However, along with the complexities of belongingness, people of similar ages, economic class, and prospective futures (higher education and/or career plans) shared similar reasons for favoring one social media platform. The different features of homophily affected their outlook of each respective site.
The effects of homophily on the diffusion of information and behaviors are also complex. Some studies have claimed that homophily facilitates access information, the diffusion of innovations and behaviors, and the formation of social norms. Other studies, however, highlight mechanisms through which homophily can maintain disagreement, exacerbate polarization of opinions, and lead to self segregation between groups.
As online users have a degree of power to form and dictate the environment, the effects of homophily continue to persist. On Twitter, terms such as “Stan Twitter”, “Black Twitter”, or “Local Twitter” have also been created and popularized by users to separate themselves based on specific dimensions.
Homophily is a cause of homogamy—marriage between people with similar characteristics. Homophily is a fertility factor; an increased fertility is seen in people with a tendency to seek acquaintance among those with common characteristics. Governmental family policies have a decreased influence on fertility rates in such populations.
