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Description: A recent study showed the importance of tornado energy as a factor in a model for tornado deaths and injuries (casualties). The model was additive under the assumption of uniform threat. Here we test two explicit hypotheses designed to examine this additive assumption. The first hypothesis concerns energy dissipation's effect conditional on population density and the second concerns population's effect conditional on energy. Both hypotheses are tested using a regression model that contains the product of population density and energy dissipation. Results show that the elasticity of casualties with respect to energy dissipation increases with population density. That is, the percentage increase in casualties with increasing energy dissipation {\it increases} with population density. Similarly, the elasticity of casualties with respect to population density increases with energy dissipation. That is, the percentage increase in casualties with increasing population density {\it increases} with energy dissipation. Allowing energy and population elasticities to be conditional rather than constant provides a more complete description of how tornado casualties are influenced by these two important factors.