Social Networks and Going Viral

Network analysis is often used to understand the behavior of groups of people. Relationships within a group of people form a kind of network—a social network. Social networks are some of the longest-studied in network science, and provide some of the results most directly applicable to everyday life. This chapter will introduce you to the elementary results in social network analysis.

Topics in this chapter include the following:

• Social networks: The history of social networks in network science
• Strong and weak ties: How to interpret and quantify the intensity of relationships
• The small world problem: Understanding how very large networks can be spanned by relatively short paths
• Contagion: How information, diseases, and anything else spreads over networks

Social networks

The defining feature of social networks is that nodes represent people. The networks themselves can represent anything from small informal friend groups to entire societies.

Edges in a social network represent a type of relationship between people. Often, this relationship is friendship or communication. However, it can also be something as abstract as the similarity in their video streaming behavior. Just imagine; you might never have met someone, but you could be the only two people in the world who enjoy watching videos of sleeping hippos. That is certainly a kind of relationship!

Many of the tools of network science come from the study of social networks in sociology. The sociologists, Jacob L. Moreno and Helen Hall Jennings, developed the techniques of sociometry, a precursor to modern social network analysis and network science (Moreno And Jennings, 1934...

Strong and weak ties

In social networks, not all relationships are created equal. You might cosign a loan application for your sibling, but probably not for your cousin's babysitter's dentist's chimney sweep. In sociology, the strength of a relationship is captured by the concept of tie strength. In this context, a tie is some kind of an interpersonal relationship, and the strength is any measure of how intense or intimate that relationship is.

In 1973, the sociologist Mark Granovetter described the importance of weak ties in bridging different communities. If all ties within a community are strong, then any ties between communities must be weak. He described this phenomenon as the strength of weak ties. By bridging different communities, weak ties make it possible to find information from distant parts of a network. But how do we measure tie strength?

...

The small world problem

In 1967, the social psychologists Jeffrey Travers and Stanley Milgram sent letters to groups of people in Wichita, Kansas, and Omaha, Nebraska. They also chose a single target individual in Massachusetts. Each letter recipient was instructed to forward their letter to an acquaintance who was most likely to know the target individual. Many of the letters reached the target, and the researchers were able to find out how many steps it took. The medium number of hops was six, hence, the common phrase six degrees of separation.

Ring networks

Typically, most of an individual's acquaintances are others who live in the same area. If every individual was only acquainted with others who lived near them,...

Contagion – how things spread

So far, it's been a lot of fun calculating numbers and arranging them into nifty little tables, but what's the point? It turns out that properties such as clustering and path length are incredibly important for social processes! In particular, they're important for contagion: the spread of ideas, disease, or anything else that moves from person to person. Understanding how network structure influences the spread of diseases and ideas makes it possible to

Simple contagion

A simple contagion is a social process in which each individual becomes infected after a single exposure. Simple contagions are good models for highly contagious diseases, or the spread of uncontroversial...

Summary

Social networks are one of the most compelling applications of network science. From the early days of sociometry to the more recent social network analysis, concepts from network science have helped uncover insights about groups of people and how they interact. Tie strength can be used to find weak ties that predict how communities might split and that enable information to spread across distant regions of a network. Small world networks resolve the paradox of small paths across networks of local connections. All of these structural properties have important implications for contagions: the spread of things such as ideas and diseases across groups of people. The concepts learned in this chapter are crucial for understanding how people behave and interact in groups. If you liked simulating contagions in this chapter, you'll love the next one! It's all about simulating...

References

The following is a list of resources that you can consider to get further knowledge:

• Granovetter, M. S. (1977). The strength of weak ties. In Social networks. Academic Press.
• Moreno, J. L., & Jennings, H. H. (1934). Who Shall Survive? Nervous and Mental Disease.
• Travers, J., & Milgram, S. (1967). The small world problem. Psychology Today, 1(1).
• Watts, D. J., & Strogatz, S. H. (1998). Collective dynamics of ‘small-world’ networks. Nature, 393(6684).
• Zachary, W. W. (1977). An information flow model for conflict and fission in small groups. Journal of anthropological research, 33(4).