Friendship isn’t always as serendipitous as it might feel; according to new research, there are just three ways people typically structure their social lives.

When striking up new connections, people are either “tight-knitters,” “compartmentalizers,” or “samplers,” according to Dartmouth sociology professor Janice McCabe, whose study of the effects of social connections on academic performance was published this month in the journal Contexts. McCabe used mathematical models to examine the friendship structures of 67 students on a Midwestern college campus, aiming to figure out how those structures influenced success in the classroom.

In doing so, she also drew out three distinct models of friendship—unlikely to be limited to college students alone. According to McCabe, people tend to be one of the following three types of friendship-makers:

A tight-knitter. (Courtesy of Janice McCabe/Dartmouth)

Tight-knitter: You have one dense group of friends in which nearly everybody knows one another. The network, which visually looks like a ball of yarn, can offer immense social support to those within it—but members are also at risk of “pulling each other down.”

A compartmentalizer. (Courtesy of Janice McCabe/Dartmouth)

Compartmentalizer: You have two to four “clusters” of friends who don’t know each other; one “cluster” may comprise people you have fun with, while another could be made up of people whom you turn to for work-related support or advice.

A sampler. (Courtesy of Janice McCabe/Dartmouth)

Sampler: You have one-on-one friendships, rather than groups of friends, and don’t rely on friendships for a sense of belonging. You achieve success without the help of others, but may feel socially isolated.

McCabe, who is publishing her research in a book next month, tells Quartz she is planning to delve further into the topic to tease out the specific reasons people lean toward one model of friendship over another. One possible factor is race: Her study on college students found that black or Hispanic students tended to be tight-knitters, while their white peers were more likely to be compartmentalizers. But surely demographics aren’t the only influencers, McCabe says, adding: “Is it something about personality? It seems to me there’s something underneath it.”

Recognizing one’s own friendship-making style may prove useful, especially for those completely unaware of their social surroundings—which means most people.