An input/output table presents the supply (production) and use (consumption) of goods and services (products) between all activities of an economy and the primary factors involved in that production, in a tabular format. These tables form the foundation of input/output economics, a quantitative economic technique that captures the interdependencies between different sectors of an economy.
Input/output tables originated with the work of economist Wassily Leontief in the 1930s and have since become fundamental tools for economic analysis and environmental modelling. In the context of Life Cycle Assessment, input/output tables provide a systematic representation of the flows of products between economic activities, making them particularly valuable for constructing comprehensive life cycle inventories that account for all upstream production chains.
The structure of an input/output table typically consists of rows representing the outputs (supply) from each activity and columns representing the inputs (use) required by each activity. This matrix format reveals not only direct relationships between activities but also enables calculation of indirect effects throughout the entire economic system. The tables also include primary factors of production such as labour costs, net taxes, net operating surplus, and rent, which represent exchanges between the economy and the broader environment.
In LCA databases and methodology, input/output tables are closely related to supply-use tables, which combine a supply table and a use table with activities on one axis and products on the other. The supply table records data on the supply of products from each activity, whilst the use table records data on the use of products by each activity. Together, these provide the average, linear production function of an activity, showing what production factors (inputs) are used to produce the outputs of an activity.
When transformed and linked through specific system modelling procedures, input/output tables become direct requirements tables, which represent linear, homogeneous steady-state models of the economy and environment. This transformation allows practitioners to trace the full life cycle implications of changes in demand for specific products throughout interconnected economic activities.
