  Triadic closure has been conceptualized and measured in a variety of ways,
most famously the clustering coefficient. Existing extensions to affiliation
networks, however, are sensitive to repeat group attendance, which manifests in
bipartite models as biclique proliferation. Whereas this sensitivity does not
reflect common interpretations of triadic closure in social networks, this
paper proposes a measure of triadic closure in affiliation networks designed to
control for it. To avoid arbitrariness, the paper introduces a triadic
framework for affiliation networks, within which a range of measures can be
defined; it then presents a set of basic axioms that suffice to narrow this
range to the one measure. An instrumental assessment compares the proposed and
two existing measures for reliability, validity, redundancy, and practicality.
All three measures then take part in an investigation of three empirical social
networks, which illustrates their differences.
