164 Ewert and Selzer
the study of Wolfgang Reinhard5 on the entanglement of Roman city elites in
the sixteenth and seventeenth centuries was a sort of milestone, as it was the
first time that the methodology and potential of social network analysis were
presented in a historical context.
A Brief Sketch of the Method of Social Network Analysis
With the formation of social network theory, formal methods to describe
the structure of networks were introduced into sociological research.6 These
techniques were derived from graph theory, group theory, and matrix algebra.
A set of relationships of a certain number of persons is depicted in a graph.
The graph’s nodes represent individuals, and its edges represent the relations
found between them.7 Two structural measures are typically calculated from
such a mathematical representation of a network. The network’s overall den-
sity is the actual relationships’ (edges) share of the number of all relations
possible.8 The more potential connections there are between individuals, the
more dense the network is. Centrality measures how easy it is for a network
member to get in contact with other participants of the network. Path dis-
tances within the network are commonly used for this.9 For example, a person
who has personal relationships with every other member would obtain the
highest possible degree of centrality because he can reach everyone directly.
Since in sociological research, networks are often constructed using sampling
and survey techniques, problems of measurement error, validity, and reliabil-
ity of the data can arise. Analyses of historical social networks are naturally
restricted to those pieces of social structure documented in the surviving
sources. Therefore, shortcomings of the data may cause difficulties as well. As
re-sampling of new data is impossible in historical research, problems that
arise because of limited or biased data can only be overcome with a careful
interpretation. In applying the network concept to historical networks, it is
5 Wolfgang Reinhard, Freunde und Kreaturen: “Verflechtung” als Konzept zur Erforschung his-
torischer Führungsgruppen. Römische Oligarchie um 1600, Schriften der Philosophischen
Fachbereiche der Universität Augsburg, vol. 14 (München: Ernst Vögel, 1979).
6 An overview of techniques used in social network analysis can be found in Bruno Trezzini,
“Konzepte und Methoden der sozialwissenschaftlichen Netzwerkanalyse: Eine aktuelle
Übersicht,” Zeitschrift für Soziologie 27 (1998), 378–394.
7 Peter Kappelhoff, “Cliquenanalyse: Die Bestimmung von intern verbundenen Teilgruppen in
sozialen Netzwerken,” in Pappi, ed., Methoden (see footnote 1), 39–63, 39–43.
8 Pappi, “Einleitung” (see footnote 2), 28.
9 Linton C. Freeman, “Centrality in Social Networks: i. Conceptual Clarification” Social
Networks 1 (1978/79), 215–239; Pappi, “Einleitung” (see footnote 2), 25–36.