Before revision:  Unlike other measures, modularity-impact is signed, providing additional information about each node's role : hub within its community , or bridge between communities. We analyze our results in a network robustness framework, as it is a generalized version of immunization under SIR models, which prior works have used for evaluation. We show that our measure out-performs previous measures for immunizing strategies in generated networks with strong community structure. Additionally, we show that our measure gives the most effective attack strategy for a million-node infrastructure network, fragmenting it while removing less than 2\% of nodes. This is over 8 times more fragile than can be seen with previous group-centralities.
After revision:  Unlike other measures, modularity-impact is signed, providing additional information about each node's role as a community bridge or hub. We derive a computationally efficient method of calculating modularity vitality for all nodes in O(M + NC) time, where C is the number of communities. We systematically fragment networks by removing central nodes, and find that modularity vitality consistently outperforms existing community-aware centrality measures. Modularity vitality is over 8 times more fragile than can be seen with previous group-centralities.