How many friends do you have?

How many people do you know? How many friends do you have? You may have tried to count your contacts on Facebook or other social networking websites. You may even have felt a bit weird realizing that your “real” friends — those you can rely on — are just a handful. As unexpected it might seem, business professionals have this question in mind too: they want to get a sense of the potentially useable social capital of their associates and employees.

Social research has investigated this matter intensely and can offer insight. There are, in fact, two aspects to be considered: the size of personal networks and the effects of online communication on socialisation.

The size of personal networks

A personal network. Hollow circles represent face-to-face contacts, filled circles represent online contacts. Green = emotionally intimate, blue = very close, yellow = close, red = not-so-close.
A personal network. Hollow circles represent face-to-face contacts, filled small circles represent online contacts, nested circles are both face-to-face and online. Green = emotionally intimate, blue = very close, yellow = close, red = not-so-close.

Let us first start with the size of personal networks. A milestone in this debate is the so-called “Dunbar’s number“, based on a 1992 study of Oxford anthropologist Robin Dunbar. The idea is that human cognitive capacities as measured by the size of the neocortex lead to a network size of around 148 (with some range of variation). The original study compared the size of the neocortex in various groups of primates and humans and referred to cohesive communities. The resulting limit indicates the number of people with whom one can maintain “stable” social relationships, i.e., know who each contact is, and how they are related to one another.

Other parts of the brain may be involved too, suggest neuroscientists: Lisa Barrett and her co-authors (2010) found a correlation between amygdala volume and social network size in humans. (I understand that the amygdala is the part of brain that regulates emotional responses and aggression, while the neocortex to which Dunbar referred is the part of the brain that presides higher mental functions.) (see this Blogpost for further information).

In social network analysis perspective, it is also important to define which social network we are measuring. Peter Marsden (1987) distinguished “core” networks from whole personal networks, pointing out that even when people have many friends, there are only a handful with whom they “can discuss important matters”. In this sense, core networks may not include more than five or six people. So if you thought you had very few friends, you shouldn’t feel weird after all… apparently the Portuguese have a saying, “You have five friends, and the rest is landscape.”

On the other hand, your full network also including mere acquaintances and weaker ties may be much larger than Dunbar’s: counts of full networks taken by Peter Killworth, H. Russel Bernard, Chris McCarthy and co-authors in the 1990s – 2000s went up to about 1500 for the average American. From these, they extracted more meaningful measures of networks that are really relevant for people’s daily lives and came up with other numbers: they found a mean personal network size of 290 (twice the Dunbar number!); more recently, Matthew Salganik and his co-authors (2010) have come up with an even larger size of 610 (twice Killworth’s number…).

Overall, an issue that emerges from many of these discussions is that cognitive capacities (however defined) matter primarily because they are associated with a basic limitation of all living beings –time is finite. Therefore, increasing the size of one’s personal network implies that less time is available for each contact: the size of the overall network increases, but the size of the core network doesn’t. Weak ties may gain at the expense of strong ties.

Online communications and socialisation

A small personal network. Legend: as above.
A small personal network. Legend: as above.

But then, what about the effects of social networking sites such as Facebook, MySpace and so on? Let’s now look at the debate on the socializing or de-socializing effects of computer-mediated communication. In a controversial article on the “Internet paradox” (1998), Robert Kraut and co-authors suggested that the more time users devote to web-based interactions, the more they lose contact with family and close friends. In this perspective, the Web would exacerbate the trade-off between weak ties (supposedly online) and strong ones (supposedly offline). Yet the authors themselves came to more nuanced conclusions a few years later, with their “The Internet paradox revisited” (2002) in which they admitted that what they observed was probably a temporary effect, and that it varied significantly with individual characteristics (gender, age etc.). Subsequent studies, starting from those of Barry Wellman and co-authors (2001), have rather tended to emphasize how Internet is a complementary form of socialization; recently, a growing body of results have stressed the positive effects of the Web especially for persons for whom socialization is a challenge (those with illnesses for example).

And for curiosity, how many friends do people actually have online? In 2009, The Economist reported figures from Facebook’s researcher Cameron Marlow, who found that the average number of Facebook friends was around 120 (though it was slightly higher for women than men). In 2012, the Pew Internet Research Center estimated that the average size of Facebook networks had increased to 229; in February 2014, this figure had further increased to reach an average of 338, with a median of 200. However, direct interactions are with a more restricted subset of friends: people leave comments for no more than 10 friends on average, and communicate by email or chat with no more than 6.

In 2011, Robin Dunbar and co-authors came back to the issue of the size of personal networks, relating it to online socialisation too. They asked whether Facebook and other social networking and instant messaging services increase personal network size; and whether they increase overall strength of ties. The answer to both questions is NO. Interestingly, their article defines personal networks as sets of three concentric circles, labelled support, sympathy, and active networks, depending on two key variables: frequency of contacts and degree of perceived emotional closeness. The sample includes mainly students, and the question of time and cognitive constraints is explicitly posed. It is said, in particular, that constancy of network size is largely due to limited leisure time.

Open questions

A personal network in which no contacts are both offline and online. Legend: as above.
A personal network in which no contacts are both offline and online. Legend: as above.

One question that arises, then, is whether networking is just leisure — or can it result from a mix of leisure and professional motivations? Dalton Conley proposes the notion of “weisure” (2009) to indicate a societal shift towards activities that combine work and leisure (including social networking with colleagues who are also friends). The organisational literature suggests that social networking may yield distinct career advantages (Burt 1992, 2005). What would happen, then, with a sample of respondents who are mainly professionals rather than students, and may be networking to do an investment in view of a reward: would we find a larger network size and/or stronger ties?

Another important issue is the distinction between the different layers of a social network — is frequency of contact really important? How related is it to emotional closeness? Would a population of migrants who have sporadic contacts with their families in the countries of origin, feel less close to them? Again, replicating the study with different populations of respondents may raise different issuees and perhaps lead to different results.

A broader issue is the degree of overlap between offline and online networks — much research is being done at the moment on this topic, but further work is certainly necessary.

So in sum, how many friends do you have?


Bickart, K., Wright, C., Dautoff, R., Dickerson, B., & Barrett, L. (2010), Amygdala volume and social network size in humans, Nature Neuroscience, DOI: 10.1038/nn.2724
Conley, D. (2009), How We Got from the Company Man, Family Dinners, and the Affluent Society to the Home Office, BlackBerry Moms, and Economic Anxiety, Pantheon.
Dunbar, R.I.M. (1992), Neocortex size as a constraint on group size in primates, Journal of Human Evolution, 22 (6): 469–493.
Killworth, P., Johnsen, E., Bernard, H. R., Shelley, G., & McCarty, C. (1990), Estimating the size of personal networks, Social Networks, 12 (4), 289-312.
Kraut, R., Patterson, M., Lundmark, V., et al. (1998), Internet paradox. A social technology that reduces social involvement and psychological well-being ? American Psychologist,  53 (9): 1017-1031.
Kraut, R., Kiesler, S., Boneva, B., et al. (2002), The Internet paradox revisited, Journal of Social Issues, 58:49–74.
Marsden, P.V. (1987). Core discussion networks of Americans. American Sociological Review, 52 (1): 122-131.
McCarty, C., Killworth, P. D., Bernard, H. R., Johnsen, E., and Shelley, G. A. (2001), Comparing two methods for estimating network size, Human Organization, 60: 28-39.
McCormick, T., Salganik, M., & Zheng, T. (2010), How many people do you know? Efficiently estimating personal network size, Journal of the American Statistical Association, 105 (489), 59-70.
Pollet, T., Roberts, S., & Dunbar, R. (2011). Use of social network sites and instant messaging does not lead to increased offline social network size, or to emotionally closer relationships with offline network members, Cyberpsychology, Behavior, and Social Networking, 14 (4), 253-258.
Wellman, B., Quan-Haase, A., Witte, J., et al. (2001), Does the Internet increase, decrease or supplement social capital? Social networks, participation and community commitment, The American Behavioral Scientist, 45:436–65.

This is a revised and updated version of a post originally published on 14 May 2011. Thanks to Antonio A. Casilli, Miriam Notten and all those who with their comments, have helped improve it over time.

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