Services contribute a little over 60 per cent of the country's GDP, yet there is no separate index to calculate growth in tertiary sector output, while that on industrial production comes every month.
To fill this void, the government has begun a process of coming out with the data on, to begin with, rail and air traffic.
The ministry of statistics and programme implementation has sought feedback on its methodology for calculating the new Index of Services Production (ISP) on these two segments.
"The ministry is likely to come out with data on these two services shortly on an experimental basis," T C A Anant, chief statistician and secretary in the ministry, told Business Standard.
Currently, HSBC purchasing managers' index somewhat captures services growth in India.
But it only gives a broad indicator to services growth month-on-month on the basis of a survey of some 500 private sector firms.
However, experts said it would take a long while for India to come out with an index for services production.
A note brought out by the ministry also said a major limitation of the existing statistical system on services is the absence of an organised mechanism for maintaining a regular database for this sector.
"Unlike the Annual Survey of Industries that is devoted to collection of data from manufacturing and a few other categories of units included in the lists maintained by the Chief Inspectors of Factories, there is no such scheme in the services sector for annual collection of data from the units," the note said.
The ministry hopes the envisaged development of a National Business Register, based on the Sixth Economic Census, is likely to address this issue to a large extent.
The suggested methodology for the two services mentioned would calculate the volume of traffic as compared to the base year of 2004-05, so set to make it comparable with other macro economic data.
The data on gross domestic product or the Index of Industrial Production have this as the base year.
"It will give indicative numbers, though these may be off the mark for a few months, but surely the Central Statistical Office has rolled the ball," said Arun Singh, senior economist, Dun and Bradstreet.
Initially, the unorganised sector which contributes nearly 40 per cent to services and may not be considered in calculating ISP.
Anis Chakravarty, director, Deloitte, Haskins and Sells, notes that even in calculating GDP numbers, the unorganised sectors are not tracked.
Madan Sabnavis, chief economist, CARE Ratings, said, "Unorganised sector data is anyway based on sample surveys, again not reliable."
He added the ISP would be able to provide the actual trend only if the numbers were revised continuously.
The weights of various components of the two services have been assigned on the basis of revenue earned data, which is readily available.
The methodology was adopted by a technical advisory committee under the chairmanship of C P Chandrasekhar, professor at Jawaharlal Nehru University, Delhi.
The TAC had advised compilation of the index for different sub-sectors of the economy in a phased manner, with priority given to some like railways, air transport, postal services, banking, telecommunication, etc, which are more organised in terms of availability of data.