In economics, an input–output model is a quantitative economic model that represents the interdependencies between different sectors of a national economy or different regional economies. They are based on are formalized as industry-by-industry or product-by-product Matrices, where rows typically represent outputs from one sector to another, and columns represent inputs. These models are often used by national statistics offices for their system of national accounts, including the quantification of Gross domestic product. Furthermore, they have been used increasingly in recent years to quantify Environmental footprints, enabling a consumption-based accounting of environmental impacts. Because they are linear in nature, computing input-output models is computationally cheap. However, they require large amounts of data and are therefore often subject to delays and sometimes uncertainties. Wassily Leontief (1906–1999) is credited with developing this type of analysis and was awarded the Nobel Prize in Economics for his development of this model.