Base-Year Revision in National Accounts

A base year is the reference year whose prices are used to value output in constant-price national accounts. Holding prices fixed means that changes in real GDP primarily represent changes in the volume of goods and services rather than inflation. The base year is revised periodically because an old price and production structure becomes less representative of the economy.

Why the base year is revised

Base-year prices act as implicit weights in combining diverse goods and services. As production, consumption, technology and relative prices change, old weights can misrepresent the contribution and growth of different activities.

• New products, services and emerging sectors may be inadequately represented in an old series.
• Declining activities may retain excessive importance when valued using outdated relative prices.
• A recent, reasonably normal year with adequate and reliable data provides a more representative benchmark.

What rebasing changes

A base-year revision generally incorporates newer and more comprehensive information, rather than merely changing reference prices. Because weights, coverage, data and methods may change together, rebasing can revise both GDP levels and measured growth rates.

• Latest surveys, administrative records and other databases can improve estimates of output, inputs and value added.
• Revised classifications, concepts and estimation methods can align the accounts more closely with the System of National Accounts framework.
• Current-price and constant-price estimates coincide in the new base year, subject to the same accounting framework.
• Rebasing improves relevance and measurement, but it does not remove all statistical errors or make real GDP a measure of welfare.

Why a back series is necessary

A back series reconstructs estimates for earlier years, as far as available data permit, using the new series' concepts, coverage, methods and price structure. Without it, figures before and after rebasing may embody different statistical frameworks, creating a break that can be mistaken for an economic change.

• It permits meaningful comparison of GDP levels and growth rates across the old and new series.
• It supports consistent analysis of long-term growth, structural change and business cycles.
• It allows historical ratios that use GDP as a denominator to be interpreted on a comparable basis.