Real GDP is a chain-volume series expressed in 1995/96 prices. Statistics New Zealand publishes both a production- and expenditure-based GDP series. Conceptually, both series are the same. However, as each series uses independent data and estimation techniques, some differences between the alternative measures arise. The expenditure-based series has historically shown more quarterly volatility and is more likely to be subject to timing and valuation problems. For these reasons the production-based measure is the preferred measure for quarter-on-quarter and annual changes.