We present an approach to vertex centrality that measures the impact of a vertex
in a graph
by removing it and considering
the subgraph
. Various
parameters can be calculated for
and compared with the corresponding parameters for
to
obtain a ranking of the vertices. The parameter examined in this paper is the largest
eigenvalue of the adjacency matrix of the graph. Previous work demonstrates the tight
relationship between this invariant, the birth and death rates of a contagion spreading
on the graph, and the trajectory of the contagion over time. We begin by conducting a
simulation to examine the validity of this claim. Subsequently, we introduce a new
centrality measure that we call the spread centrality. The spread centrality of a vertex
in a graph
is the difference between
the largest eigenvalues of
and
. In
some, but not all, cases the vertex rankings given by spread centrality and eigenvector
centrality are correlated; we provide examples of both.