Critical infrastructure dependency assessment using the input–output inoperability model

The input–output inoperability model (IIM) is a simple, but powerful, mechanism for analyzing the cascading effects induced by critical infrastructure dependencies and interdependencies. IIM typically uses financial data as a measure of the dependency phenomena. Since financial data is only one of the many dimensions for analyzing dependency phenomena, the quality of IIM parameters and, thus, the reliability of IIM results can be affected negatively. This paper proposes a methodology for evaluating IIM parameters based on technical and operational data. The data is collected by interviewing experts and is processed using a fuzzy set based methodology. A case study involving Italian critical infrastructure sectors is used to demonstrate the effectiveness of the methodology.