40 Famous Friendship Studies Summarized in Two Sentences or Less

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Social Research From the 1960’s Until Now

Prior to the 1980’s, researchers focused more on the influence of parents and family systems, and rarely studied how social relationships impacted a person’s life or well being (Blieszner and Adams, 1992). However, the field of “friendship”–so to speak–has picked up steam in the last several decades and yielded more insights about how people connect to each other.

Below, you’ll find a timeline of 40 important studies related to social life, including a summary of the insights each unearthed (such as the idea that everyone is separated by seven degrees).

The 1960’s

  • (1960s) Yale professor Stanley Milgram’s now famous experiment theorized that all people are connected by six degrees.
  • (1969) John Bowlby showed how childhood caregivers may set the stage for whether a person develops healthy attachments later in life.

The 1970’s

  • (1973) Sociologist Mark Granovetter identified factors that foster strong connections between people. They include time, intimacy, and reciprocation.
  • (1975) Weiss and Lowenthall found circles of friends usually decrease in size as a person ages, due to the demands of family and work.
  • (1977) Psychiatrist George Engel expanded traditional ideas about the causes of human illness. He suggested factors went far beyond genes and physical body systems to include social factors like relationships and beliefs.

The 1990’s

  • (1992) Ohio University Professor Bill Rawlins establishes five criteria that define friendship: affection, voluntary connection, mutual likeability, equal footing, mutual participation. He also wrote The Compass of Friendship.
  • (1992) Robert Dunbar suggested the human brain only has the capacity to maintain relationship with around 150-230 people at one time.
  • (1999) Harvard researcher Morton Hansen discovered that weak social links were surprisingly powerful because of the role they played in transferring information, teaching, idea-generation, and more.

The 2000’s

  • (2000) Author Robert Putman, who published Bowling Alone: The Collapse and Revival of American Community, concluded that social connectivity had declined in recent decades.
  • (2001) Psychiatrist Daniel Siegel popularized the phrase “interpersonal neurobiology” to show how people’s connectedness impacted their brain function.
  • (2002) Thomas Burndt and Lonna Murphy put together this exploration of friendship which explores how children are influenced by their friends.
  • (2003) Blau and Fingerman suggest that “consequential” strangers play an important role in our lives because they influence our moods, anchor us, and even prompt developmental growth.
  • (2004) Blieszner and Roberto found most people consider friends to be voluntary relationships that hold meaning across the course of their lives. They found the necessary prerequisites for bonding included repeated  and frequent interactions (in pairs or small groups) and enough privacy to promote safe sharing and self-disclosure.
  • (2004) An Australian study conducted over 10 years found that older people with a large number of friends were noticeably less likely to die than those with fewer friends.
  • (2005) Daniel Goleman, popular author and psychologist, helped the larger culture embrace the idea of social intelligence, which explores how awareness and social skills lend to people’s overall life success.
  • (2005) Researchers Newman and Dale discovered there are people who often serve as bridges to groups of diverse friends unlike themselves.
  • (2006) Tom Rath, in his Gallup book Vital Friends, examined how friendships (or the lack there of) has deep impact on the course of one’s life. His work includes interesting insights about how people are influenced by the behaviors of their friends.
  • (2006) Psychotherapist Louis Cozolino wrote The Neuroscience of Human Relationship suggests the brain evolved over time to produce language, which enhanced people’s ability to bond with each other.
  • (2006) Communications consultant Tim Sanders released the Likeability Factor (L-Factor), in which he suggests a person can learn how to be likeable.
  • (2007) Researchers found a strong link between a person’s obesity and their friends’ weight. Risk for obesity increased nearly 60% when one’s friends were gaining weight.
  • (2007) Ellison, Steinfeld, and Lampe found people have more face-to-face interactions with offline friends, while online connections increased their potential ability to bond.
  • (2009) Researchers studied people’s intrigue with their friends’ photos posted on social media. Social media, they found, prompted curiosity about other people’s lives and triggered feelings of jealousy or comparison.
  • (2009) Christakis and Fowler studied the degree to which people influence their own friends, as well as how they influence their friends’ friends and friends of their friends’ friends (third degree connections).
  • (2009) The Pew Internet and American Life Project found people typically have fifteen friends they deem “close” and sixteen friends they deem “less close”.
  • (2009) Muis, Chrisfides, and Desmarais found jealousy and other emotional states may be linked to or impacted by the use of social networking sites, especially for teenagers.

The 2010’s

  • (2010) In The Girls From Ames: A Story of Women and a 40-Year Friendship, author Jeffrey Zaslow chronicled the lives of 11 childhood friends who moved from Iowa to different places around the United States. He followed them through college, marriage, divorce, and other tragedies, including one woman’s death in young adulthood.
  • (2010) Researchers Wang and Wellman demonstrate how the introduction of new technology (whether it be radio, telephone, television, or other) has always caused concern about the quality of civic life. He found these challenges are not new or related only to the dawn of the internet.
  • (2010) Anthropologist Robin Dunbar found that new friends often displace other friends already in a person’s close friend network.
  • (2011) University of Pennsylvania researchers showed people value the people who most value them. They also looked at the motives behind friendship and whether people form connections because of the advantages/protections they receive from personal alliances.
  • (2011) Slotter and Gardner found people select friends based on both obvious, conscious traits as well as subconscious ideas like whether or not people help us grow toward our aspirations.
  • (2011) Van der Horst and Coffe explored the connection between strong social networks and how people assessed their well-being.
  • (2011)Dr. Charity Friesen of Wilfrid Laurier University discovered that friendships succeed in part based on people’s ability to be aware of what irritates their friends.
  • (2012) Carl Zimmer explored the possibility that other species, besides humans, might experience friendship and traits like loyalty and compassion.
  • (2012) Researchers delved into the little studied phenomena of platonic friendships with members of the opposite sex. They found men were more attracted to their female friends than the women were to them. Men also tended to guess women were more interested in them than they actually were.
  • (2012) New York Times writer Alex Williams wrote “Friends of a Certain Age” which pinpointed barriers to friendship such as busy schedules, i.e. the lack of time.
  • (2012) Cotton, Ford, Ford, and Hale found older adults who use online social netorks are 20-28% less likely to become depressed.
  • (2012) University of Wisconsin researchers Lauren Jelenchick and Megan Moreno argued previous research claims that teen’s internet use was linked to depression could not be proven.
  • (2012)Researchers at Department of Epidemiology and Public Health at University College London found marriage benefits men’s social health as it often fosters strong social support, while women’s social networks tend to decrease in size due to the demands of marriage.
  • (2013) University of Virginia researchers discovered that humans have a deep sense of empathy. When people’s friends are threatened, they feel the same sense of fear or danger their friend who is actually experiencing the threat feels.
  • (2014) The National Academy of Sciences explored how people tend to choose friends that are genetically similar to themselves.
  • (2014) A study published by social networking site, LinkedIn, found that friendships in the office are often discolored slightly by competition. (They found, for example, that 68% of people born since 1980 would be willing to lose one of their friendships to earn a promotion.)

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  1. gapaul

    I was looking for just one study so I feel like I hit the jackpot. Thanks for compiling these. It’s going to make a presentation I have to give tomorrow sooooo much easier.

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