Supply- and Output-Side Extensions to the Inoperability Input-Output Model for Interdependent Infrastructures

The Inoperability Input-Output Model (IIM) was developed to help understand infrastructure interdependencies. Based on the Leontief Input-Output Model, the IIM approximates the physical interdependencies of infrastructures from the economic input-output transactions of sectors. The model is demand-driven, wherein perturbations to the final demand levels are considered the initiating event, and the impact to sectors’ production outputs are the direct and indirect effects resulting from sector interdependencies. This paper presents two other perspectives—supply-side and output-side—to supplement and complement the demand-driven IIM. These two perspectives help address initiating perturbations related to input factors (value added) and to the sectors’ output levels. Further, these perturbations can be in terms of either quantity or price changes, defining the demand-quantity and supply-price models. Finally, the demand-, supply-, and output-side models are integrated using a sequential perturbation approach. A case study using the Virginia 1997 I-O accounts is presented, where it was shown that the different perturbation classes (demand or supply, quantity or price) yield different rank orders of sectors impacted by the initiating event, thus providing various perspectives of impacts.