Input-Output Tables (IOTs) describe the sale and purchase relationships between producers and consumers within an economy. They can either illustrate flows (sales and purchases) of final and intermediate goods and services defined according to industry outputs (i.e. industry x industry tables) or according to product outputs (product x product tables).

The OECD Input-Output database is presented on the former basis, reflecting in part the collection mechanisms for many other data sources such as Research and Development expenditure data, employment statistics, pollution data, energy consumption, which are mainly collected by enterprise or establishment, and thus according to industry classifications.

The indicator imports content of exports represents the degree of vertical specialization. The contribution that imports make in the production of exports of goods and services.

Imports content of exports = u Am (I - Ad)^-1 EX / Σ EX, where:
• Am and Ad are the input-output coefficient matrices for imported and domestic transactions, respectively,
• I is the identity matrix,
•u denotes an 1 x n vector each of whose components is 1 for corresponding import types,
• and EX is the export vector.