Homophily

Baseline vs. inbreeding

To test the relevance of homophily researchers have distinguished between baseline homophily and inbreeding homophily. The former is simply the amount of homophily that would be expected by chance given an existing uneven distribution of people with varying characteristics, and the second is 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, Lazarsfeld and Merton (1954) distinguished between status homophily and value homophily.

The authors find that individuals with similar social status characteristics are more likely to associate with each other than by chance. "Status" includes both ascribed characteristics like race, ethnicity, sex, and age; and acquired characteristics like religion and education. In contrast, value homophily involves association with others who think in similar ways, regardless of differences in these status characteristics.

Race and ethnicity

Social networks in 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, and this tends to give racial and ethnic minority groups a higher baseline homophily. Race and ethnicity also correlates with educational attainment and occupation, which increase baseline homophily further.

Sex and gender

With 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.

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 homophily and inbreeding.Template:How so

Education, occupation and social class

Family of birth accounts for considerable baseline homophily with respect to education, occupation, and social class.

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 by 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 (for example all heads of HR departments will tend to associate with other HR heads), family (for example 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.

Effect of homophily

One study reported that perception of interpersonal similarity improves coordination and increase the expected payoff of interactions, above and beyond the effect of merely "liking others". Another study claimed that homophily produces tolerance and cooperation in social spaces. Other studies have claimed that homophily helps people to access information, diffuse innovations and behaviors, and form opinions and social norms. Homophily influences diffusion patterns over a social network in two ways: homophily affects the way a social network develops, and individuals are more likely to successfully influence others when they are similar to them.

Homophily often leads to 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.