Introduction

In the preceding chapter, we discussed several techniques for finding cohesive subgroups within a social network. People who belong together tend to interact more frequently than people who do not. In the current chapter, we extend this idea to affective relations that are either positive or negative, for instance, friendship versus hostility, liking versus disliking. We expect positive ties to occur within subgroups and negative ties between subgroups.

Hypotheses about patterns of affective relations stem from social psychology and they are widely known as balance theory. First, we introduce this theory and discuss how it was incorporated in network analysis. Then, we apply it to affective relations, that is, social relations that are subjective and mental rather than tangible.

Balance Theory

Social psychology is interested in group processes and their impact on individual behavior and perceptions. In the 1940s, Fritz Heider formulated a principle that has become the core of balance theory, namely that a person feels uncomfortable when he or she disagrees with his or her friend on a topic. Figure 42 illustrates this situation: P is a person, O is another person (the Other), and X represents a topic or object. P likes O, which is indicated by a positive line between P and O, but they disagree on topic X because P is in favor of it (positive line), whereas O is opposed to it (negative line). Note the convention of drawing negative ties as dashed lines, which is also adopted in Pajek.