Measures of national income an output are used in economics to estimate the welfare of an economy through totaling the value of goods and services produced in an economy. They use a system of national accounting first developed during the 1940s. The primary measures of national income and output are Gross Domestic Product (GDP), Gross National Product (GNP), Gross National Income (GNI), Net National Product (NNP), and Net National Income (NNI).