Real instances of social systems have a bursty character, meaning that events occur in a clustered manner. For example, the figure below shows how rare events occur over time in texts (the first indicates rarer events than the second; the second, rarer than the third). This clustering phenomenon indicates how a sequence has long memory and thus exhibits self-similarity. We study methods for nonnumerical time series to quantify the degree of clustering and examine different self-similarity degrees across various systems.
- Long-Range Memory in Literary Texts: On the Universal Clustering of the Rare Words. Kumiko Tanaka-Ishii , Armin Bunde. PLOS One, 2016.