
15.S: Regular Equivalence (Summary)

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The regular equivalence concept is a very important one for sociologists using social network methods, because it accords well with the notion of a "social role". Two actors are regularly equivalent if they are equally related to equivalent (but not necessarily the same, or same number of) equivalent others. Regular equivalences can be exact or approximate. Unlike the structural and automorphic equivalence definitions, there may be many valid ways of classifying actors into regular equivalence sets for a given graph - and more than one may be meaningful.

There are a number of algorithmic approaches for performing regular equivalence analysis. All are based on searching the neighborhoods of actors and profiling these neighborhoods by the presence of actors of other "types". To the extent that actors have similar "types" of actors at similar distances in their neighborhoods, they are regularly equivalent. This seemingly loose definition can be translated quite precisely into zero and one block rules for making image matrices of proposed regular equivalence blockings. The "goodness" of these images is perhaps the best test of a proposed regular equivalent partitioning. And, the images themselves are the best description of the nature of each "role" in terms of its expected pattern of ties with other roles.

We have only touched the surface of regular equivalence analysis, and the analysis of roles in networks. One major extension that makes role analysis far richer is the inclusion of multiple kinds of ties (that is, stacked or pooled matrices of ties). Another extension is "role algebra" which seeks to identify "underlying" or "generator" or "master" relations from the patterns of ties in multiple tie networks (rather than simply stacking them up or adding them together).