The IIP estimate in a given month is always released within about 6 weeks from that month. The data for the IIP estimate is supplied by 15 source agencies which include Department of Industrial Policy and Promotion, Indian Bureau of Mines, Central Statistical Organisation and Central Electricity Authority, among others.

However, since most of the data regarding production might not be available at that time the index for a particular month has been created, a provisional index is first created and released, which is then updated twice in the subsequent months.

HIstory of IIP:

The IIP was first compiled and released using 1937 as the base year and included 15 industries. Subsequently, it has been updated at least seven times, both with regards to the base year as well as the nature of items included, to keep the data relevant.

In the latest norms outlined by the ministry of statistics with 1993-94 as the base year, one of the basic parameters for selection of items is that it should account for at least Rs 80 crore of gross value of output at the item level and Rs 20 crore of gross value added at the ultimate digit level.

An Improtant feature of this monthly prodcution data is that it should be continuiously available in a given sector. There have been efforts at representing the small scale and unorganised manufacturing sector.

While the items which are taken into consideration are classified into item groups under the three heads of mining, manufacturing and electricity, they have also been classified under use-based categories like basic goods, capital goods, intermediate goods, consumer durables and consumer non-durables.