Former chief statistician Pronab Sen seeks two GDP series with old, new bases for five years

India's GDP measurement methodology has been at the center of intense statistical and political debate since the Central Statistics Office (CSO), now the National Statistical Office (NSO) under the Ministry of Statistics and Programme Implementation (MoSPI), introduced a new series in January 2015 with base year 2011-12, replacing the 2004-05 base. This revision wasn't merely a routine update — it incorporated methodological shifts aligned with the UN System of National Accounts (SNA) 2008, including the adoption of Gross Value Added (GVA) at basic prices instead of GDP at factor cost, and a move toward double deflation for real growth estimation. Double deflation, the gold standard in national income accounting, requires separate price indices for inputs (Intermediate Consumption) and outputs (Gross Output) to compute real GVA accurately. However, as former Chief Statistician Pronab Sen — who headed the system during the 2004-05 base revision — has pointed out, India lacks the comprehensive Input-Output Transaction Tables and granular price data (like a robust Producer Price Index for services) needed to implement double deflation rigorously. Currently, the NSO uses single deflation with the Wholesale Price Index (WPI) and Consumer Price Index (CPI) as proxies, which can distort real growth estimates, especially when input and output prices diverge sharply, as seen during commodity price shocks. The controversy deepened with the "back series" — the recalculated historical GDP data using the new methodology. When the NSO released the back series in 2018 (after a delayed and contested process involving the NSC and NITI Aayog), it showed significantly higher growth rates for the UPA era (2005-14) than previously estimated, sparking allegations of political interference. The National Statistical Commission (NSC), established under the NSC Act, 2005 (amended 2019), is the apex advisory body on statistical matters, but its independence has been questioned. Pronab Sen's recommendation — maintaining dual GDP series (old and new base) for at least five years — is a pragmatic call for transparency and methodological validation. It mirrors international practice: when Canada and Australia revised their national accounts, they published parallel series for 5-7 years. This allows economists, policymakers, and the public to assess the impact of methodological changes, identify structural breaks, and build confidence in the new numbers. The stakes are high. GDP figures drive fiscal policy (FRBM Act targets), monetary policy (RBI's inflation-growth framework), credit ratings, and political narratives. The 15th Finance Commission (2020-25) relied on the new series for tax devolution formulas. International agencies like the IMF and World Bank use India's official data for Article IV consultations and lending decisions. A credible statistical system is also a constitutional imperative: Article 280 mandates the Finance Commission to use reliable data; Article 112 requires the Union Budget to reflect true economic conditions. The NSO's commitment to release the next back series by December 2026 — aligned with the 2017-18 base year revision (postponed due to COVID-19) — will be a litmus test for India's statistical governance. Until then, Sen's dual-series proposal offers a bridge: it acknowledges methodological evolution while safeguarding analytical continuity. For aspirants, this episode underscores a core governance challenge — balancing technical rigor, institutional autonomy, and public trust in the data that powers India's development narrative.