Childhood

The understanding of friendship in children tends to be more heavily focused on areas such as common activities, physical proximity, and shared expectations.^:498 These friendships provide opportunity for playing and practicing self-regulation.^:246 Most children tend to describe friendship in terms of things like sharing, and children are more likely to share with someone they consider to be a friend.^:246 As children mature, they become less individualized and are more aware of others. They gain the ability to empathize with their friends, and enjoy playing in groups. They also experience peer rejection as they move through the middle childhood years. Establishing good friendships at a young age helps a child to be better acclimated in society later on in their life.

Based upon the reports of teachers and mothers, 75% of preschool children had at least one friend. This figure rose to 78% through the fifth grade, as measured by co-nomination as friends, and 55% had a mutual best friend.^:247 About 15% of children were found to be chronically friendless, reporting periods without mutual friends at least six months.^:250

Potential benefits of friendship include the opportunity to learn about empathy and problem solving. Coaching from parents can be useful in helping children to make friends. Eileen Kennedy-Moore describes three key ingredients of children's friendship formation: (1) openness, (2) similarity, and (3) shared fun. Parents can also help children understand social guidelines they haven't learned on their own. Drawing from research by Robert Selman and others, Kennedy-Moore outlines developmental stages in children's friendship, reflecting an increasing capacity to understand others' perspectives: "I Want It My Way", "What's In It For Me?", "By the Rules", "Caring and Sharing", and "Friends Through Thick and Thin."

Adolescence

In adolescence, friendships become "more giving, sharing, frank, supportive, and spontaneous." Adolescents tend to seek out peers who can provide such qualities in a reciprocal relationship, and to avoid peers whose problematic behavior suggest they may not be able to satisfy these needs. Relationships begin to maintain a focus on shared values, loyalty, and common interests, rather than physical concerns like proximity and access to play things that more characterize childhood.^:246

A study performed at the University of Texas at Austin examined over 9,000 American adolescents to determine how their engagement in problematic behavior (such as stealing, fighting, and truancy) was related to their friendships. Findings indicated that adolescents were less likely to engage in problem behavior when their friends did well in school, participated in school activities, avoided drinking, and had good mental health. The opposite was found regarding adolescents who did engage in problematic behavior. Whether adolescents were influenced by their friends to engage in problem behavior depended on how much they were exposed to those friends, and whether they and their friendship groups "fit in" at school.

A study by researchers from Purdue University found that friendships formed during post-secondary education last longer than friendships formed earlier.

Adulthood

Friendship in adulthood provides companionship, affection, as well as emotional support, and contributes positively to mental well-being and improved physical health.^:426

Adults may find it particularly difficult to maintain meaningful friendships in the workplace. "The workplace can crackle with competition, so people learn to hide vulnerabilities and quirks from colleagues. Work friendships often take on a transactional feel; it is difficult to say where networking ends and real friendship begins." Most adults value the financial security of their jobs more than friendship with coworkers.

The majority of adults have an average of two close friends. Numerous studies with adults suggest that friendships and other supportive relationships do enhance self-esteem.

Older adults

Older adults continue to report high levels of personal satisfaction in their friendships as they age, and even as the overall number of friends tends to decline. This satisfaction is associated with an increased ability to accomplish activities of daily living, as well as a reduced decline in cognitive abilities, decreased instances of hospitalization, and better outcomes related to rehabilitation.^:427 The overall number of reported friends in later life may be mediated by increased lucidity, better speech and vision, and marital status.^:53

As on review phrased it:

Research within the past four decades has now consistently found that older adults reporting the highest levels of happiness and general well being also report strong, close ties to numerous friends.

As family responsibilities and vocational pressures lessen, friendships become more important. Among the elderly, friendships can provide links to the larger community, serve as a protective factor against depression and loneliness, and compensate for potential losses in social support previously given by family members.^:32-3 Especially for people who cannot go out as often, interactions with friends allow for continued societal interaction. Additionally, older adults in declining health who remain in contact with friends show improved psychological well-being.

Attention deficit hyperactivity disorder

Children with attention deficit hyperactivity disorder (ADHD) may have difficulty forming and maintaining friendships, due to a limited ability to build social skills through observational learning, difficulties attending to social cues, and because of the social impacts of impulsive behavior and a greater tendency to engage in behavior that may be seen as disruptive by their peers.^[26] In a 2007 review, no treatment was identified which effectively address peer functioning in children with ADHD, and treatments which addressed other aspects of the disorder were not found to eliminate issues related to peer functioning.^[25]

Autism

Certain symptoms of autism spectrum disorders can interfere with the formation of interpersonal relations, such as a preference for routine actions, resistance to change, obsession with particular interests or rituals, and a lack of social skills. Children with autism have been found to be more likely to be close friends of one person, rather than having groups of friends. Additionally, they are more likely to be close friends of other children with some sort of a disability.^[27] A sense of parental attachment aids in the quality of friendships in children with autism spectrum disorders; a sense of attachment with one's parents compensates for a lack of social skills that would usually inhibit friendships.^[28]

A study done by Frankel et al. showed that parental intervention and instruction plays an important role in such children developing friendships.^[29] Along with parental intervention, school professionals play an important role in teaching social skills and peer interaction. Paraprofessionals, specifically one-on-one aides and classroom aides, are often placed with children with autism spectrum disorders in order to facilitate friendships and guide the child in making and maintaining substantial friendships.^[30]

Although lessons and training may help peers of children with autism, bullying is still a major concern in social situations. According to Anahad O'Connor of The New York Times, bullying is most likely to occur against autistic children who have the most potential to live independently, such as those with Asperger syndrome. Such children are more at risk because they have as many of the rituals and lack of social skills as children with full autism, but they are more likely to be mainstreamed in school, since they are on the higher-functioning end of the autism spectrum. Children with autism have more difficulty attending to social cues, and so may not always recognize when they are being bullied.^[31]

Down syndrome

Children with Down syndrome have increased difficulty forming friendships. They experience a language delay causing them to have a harder time playing with other children. Most children with Down syndrome may prefer to watch other students and play alongside a friend but not with them, mostly because they understand more than they can outwardly express. In preschool years, children with Down syndrome can benefit from the classroom setting, surrounded by other children and less dependent on adult aid. Children with this disability benefit from a variety of interactions with both adults and children. At school, ensuring an inclusive environment in the classroom can be difficult, but proximity to close friends can be crucial for social development.^[32][33]

Studies have found that strong social supports improve a woman's prospects for good health and longevity. Conversely, loneliness and a lack of social supports have been linked to an increased risk of heart disease, viral infections, and cancer, as well as higher mortality rates overall. Two researchers have even termed friendship networks a "behavioral vaccine" that boosts both physical and mental health.^[34]

There is a large body of research linking friendship and health, but the precise reasons for the connection remain unclear. Most of the studies in this area are large prospective studies that follow people over time, and while there may be a correlation between the two variables (friendship and health status), researchers still do not know if there is a cause and effect relationship, such as the notion that good friendships actually improve health. A number of theories have attempted to explain this link. These theories have included that good friends encourage their friends to lead more healthy lifestyles; that good friends encourage their friends to seek help and access services when needed; that