The Index of Industrial Production (IIP) compares the growth in the general level of industrial activity in the economy with reference to a comparable base year. In order to capture the structural changes in the industrial sector, the base year of the all-India IIP which was commenced in India in 1937 was revised in 1946, 1951, 1956, 1960, 1970, 1980-81 and 1993-94. The current series of all-India IIP (base 1993-94) was released in May 1998.