“Methods of the input/output (I/O) category start their modeling with the description of direct links among components of a global structure (e.g. national exchanges). The direct and indirect needs of a component (e.g. economic sector) can then be accounted for to offer relevant information on the sustainability of the global structure. The general concepts underlying the I/O methods are based on the pioneer work of Leontief in the 1930’s. The main advantage of I/O based methods is the inherent completeness of analysis they allow. All flows inside the system boundary (e.g. UM) are considered and the proportion of effects from each component of a UM can be put into perspective with the global effects. For instance, if using a multi-regional I/O framework. Still, this completeness may come with coarse definition of the full system. This prevents the targeted audience of a study from choosing precise solutions to improve the sustainability of components that are found in a UM. For example, it is rather difficult to identify the type of vehicle that is responsible for the majority of GHG emissions in a city if the model only says that the transport sector is responsible for 35% of the GHG emissions from a UM. The I/O methods usually use economic flows to describe the link between components of a system. This monetary modeling does not offer information for the evaluation of environmental impacts. Therefore, other methods have been proposed to overcome this missed opportunity.” (Beloin-Saint-Pierre et al. 2016)

As becomes evident from the above description, input-output methods make up another crucial accounting family that is relevant for the quantification of resources, including materials, energy and land of a system, albeit originally stemming from expressing inter-industrial trades in monetary terms, which is the method known as input-output analysis. This method and the following four will be described in this category: Multiregional input-output (MRIO) tables, physical input-output (PIOT) tables, environmentally extended input-output analysis (EE-IOA) and throughflow analysis.