Analysing high school friendships and marriages, researchers from Graz University of Technology and the Complexity Science Hub find an unconscious principle by which we form social relationships.

Our personal identity is composed of many dimensions, such as age, gender, ethnic background, or socioeconomic status. A research team led by Fariba Karimi from the Institute of Human-Centred Computing at Graz University of Technology (TU Graz) and Samuel Martin-Gutierrez from the Complexity Science Hub developed the statistical computational model “MAPS” to calculate the influence of these factors on our social relationships. The researchers have recently published a MAPS-based analysis of high school friendships and marriages in the US in the journal Communications Physics.

Extremely selective

The study shows that humans are extremely selective: “Both when choosing high school friends and when selecting marriage partners, we evaluate all identity characteristics of other people. Only if we assess all these characteristics positively do we enter into social relationships,” says Samuel Martin-Gutierrez. If even a single identity trait is evaluated negatively, engaging in a relationship gets unlikely despite other strong similarities. “This selective behaviour explains the tendency towards the formation of highly segregated, homogeneous groups in our society,” says Fariba Karimi, who leads the Computational Social Science group at TU Graz and who member of the Complexity Science Hub faculty.

Marriage data from the 50 largest U.S. Cities

The researchers validated their MAPS model using data from the Add Health study on friendship networks, comprising a total of 41,800 high school students, as well as marriage databases from the 50 largest cities in the United States. In school friendships, grade level and ethnic background proved to be the most important drivers of long-term connections. In marriage data, age, gender, and ethnic background were the decisive factors for accurately reproducing observed marriages mathematically.

Improving Opportunities for Interaction

“Understanding the principles by which people form social relationships is essential for comprehending social dynamics and for effectively counteracting polarization of societies,” says Fariba Karimi. If cities improve opportunities for interaction among diverse population groups and for children from different backgrounds to attend school together, the likelihood of relationships across social boundaries can be systematically increased.