  Exponential-family random graph models (ERGMs) are probabilistic network
models that are parametrized by sufficient statistics based on structural
(i.e., graph-theoretic) properties. The ergm package for the R statistical
computing system is a collection of tools for the analysis of network data
within an ERGM framework. Many different network properties can be employed as
sufficient statistics for ERGMs by using the model terms defined in the ergm
package; this functionality can be expanded by the creation of packages that
code for additional network statistics. Here, our focus is on the addition of
statistics based on graphlets. Graphlets are small, connected, and
non-isomorphic induced subgraphs that describe the topological structure of a
network. We introduce an R package called ergm.graphlets that enables the use
of graphlet properties of a network within the ergm package of R. The
ergm.graphlets package provides a complete list of model terms that allows to
incorporate statistics of any 2-, 3-, 4- and 5-node graphlet into ERGMs. The
new model terms of ergm.graphlets package enable both ERG modelling of global
structural properties and investigation of relationships between nodal
attributes (i.e., covariates) and local topologies around nodes.
