Former chief statistician Pronab Sen seeks two GDP series with old, new bases for five years
A former chief statistician of India has called for two GDP series — one on the old base year and one on the new base year — to be published in parallel for five years, so users can compare the two before fully switching over.
The recommendation follows the rollout of a revised GDP series that shifts the base year and adopts "double deflation" for computing real Gross Value Added (GVA), a data-intensive method requiring separate price indices for both outputs and inputs.
Concerns were raised about whether adequate input price data — particularly an input-side Producer Price Index (PPI) — actually exists, since it remains at an experimental stage, even as an output PPI has been used for deflating output.
Nominal GDP growth under the new series was assessed as broadly credible, with the stated concern being narrower: the reliability of the price deflators that convert nominal growth into real growth.
A back series recasting historical GDP data under the new methodology is expected from the National Statistical Office (NSO) by December 2026.
Double Deflation vs Single Deflation in GVA Compilation
Gross Value Added (GVA) at constant prices can be estimated in two ways. Under single deflation, one price index (typically for the output/final product) is used to deflate the entire value added in a sector. Under double deflation, output and intermediate inputs are deflated separately using their own respective price indices, and real GVA is derived as real output minus real intermediate consumption. Double deflation is considered the more theoretically sound, internationally recommended approach under the UN System of National Accounts (SNA) framework, but it demands price data for a much larger universe of goods (all inputs, not just final products), making it far more data-intensive to implement correctly.
Key Details
- Real GVA (double deflation) = Real Output − Real Intermediate Consumption, each deflated independently
- Requires both an output-side deflator (e.g., Producer Price Index/Wholesale Price Index for finished goods) and an input-side deflator (price index for intermediate inputs)
- India's new GDP series (base year 2022-23) has expanded the number of deflators used from roughly 180 to about 600 to support this shift
- Single deflation, used in India's earlier GDP series, applies one output-based price index to the whole value-added figure — simpler but less accurate when input and output prices diverge
The core of the criticism is that double deflation is only as reliable as the input price data feeding it — if a robust, non-experimental input PPI does not yet exist, the real GVA/GDP growth numbers derived from the new methodology carry uncertainty even if nominal growth is accepted as broadly accurate.
GDP Base Year Revision — The New Series (Base Year 2022-23)
Periodically, India's GDP/GVA base year is revised to better reflect the structure of the economy — updated weights, new data sources, and coverage of activities that did not exist or were poorly captured in the old base year. The base year was last revised from 2004-05 to 2011-12 (that series was introduced in January 2015), and a new series with base year 2022-23 was released by the National Statistical Office (NSO), Ministry of Statistics and Programme Implementation (MoSPI), on 27 February 2026. Base revision is meant to occur roughly every five years, though gaps between revisions have often been longer in practice.
The proposal for two parallel GDP series (old and new base) for five years reflects this standard overlap-period practice — allowing analysts, policymakers, and RBI's monetary policy framework to cross-check the new double-deflation-based numbers against the familiar old-base series before relying on the new series exclusively.
Back Series Construction and the NSO/MoSPI Institutional Structure
A "back series" recalculates historical GDP/GVA figures using the latest base year and methodology, so that long time series remain internally consistent for analysts, the RBI, and Budget-making. In India, back-series estimates are first recomputed under the new methodology up to the point where detailed data allows, and then spliced/linked at a disaggregated level to extend the series back to 1950-51. The National Statistical Office (NSO) — formed in 2019 by merging the Central Statistical Office (CSO, established 1951) and the National Sample Survey Office (NSSO, established 1950) under MoSPI — is the body responsible for producing both the new GDP series and its back series.
Key Details
- NSO formed 23 May 2019 by merging CSO and NSSO into a single line of command under MoSPI
- CSO (compilation/standards arm) and NSSO (field survey arm) had earlier operated as separate wings, both originally under statistician P.C. Mahalanobis
- The back series linked to the new (2022-23) base year is expected to be released by the NSO by December 2026
- Back series continuity is critical for computing long-run growth rates, potential output, and for comparing pre- and post-shock (e.g., pre/post-2017) growth trajectories
Until the NSO's back series is published, only the new series (post base-revision years) exists on the new methodology, while historical comparisons still rely on the old 2011-12-base series — the exact gap that a parallel five-year dual-series release is meant to bridge.
- New GDP series base year: 2022-23; released by NSO/MoSPI on 27 February 2026
- Previous GDP series base year: 2011-12, introduced January 2015
- NSO's back series (new methodology, extended to 1950-51) expected by December 2026
- Number of deflators used in GDP compilation expanded from about 180 (old series) to about 600 (new series)
- NSO formed on 23 May 2019 by merging CSO (est. 1951) and NSSO (est. 1950) under MoSPI
- Double deflation requires separate output and input price deflators, versus a single output-based deflator under single deflation