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. This holds prices fixed so 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 an old base year becomes unsuitable

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• Declining activities may retain excessive importance when valued using outdated relative prices.
• Rebasing reduces distortions associated with using an increasingly obsolete economic structure.

Updating data and methods

A base-year revision is generally used to incorporate newer and more comprehensive information, not merely to change the reference prices.

• 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.
• A recent, reasonably normal year with adequate and reliable data provides a more representative benchmark.

Effects on the national accounts

In the new series, current-price and constant-price estimates coincide in the base year, subject to the same accounting framework. Because rebasing often changes weights, coverage, data and methods together, it can revise both GDP levels and measured growth rates.

• A consistent back series is needed to compare economic performance across the old and new series.
• Rebasing improves relevance and measurement, but it does not remove all statistical errors or make real GDP a measure of welfare.