What this covers: current and constant prices, deflation with DAC deflators, base year choice, and analyses that combine both price bases.

When to use

This reference informs questions that compare ODA across more than one year, rank donors within a year, involve adjusting for inflation, or ask why two figures for the same year differ across sources.

Concepts and definitions

Current prices (nominal) report each year's data in the price level of the year it was recorded.

Constant prices (real) report every year's data in the prices and exchange rate of one reference year. This removes the effect of donor-country inflation and of exchange-rate movements against the USD, and allows comparison of volumes across time.

The base year is the reference year of a constant-price series. With the latest year as base, the most recent year's figures are unchanged and earlier years are adjusted up or down, depending on the donor's inflation and its currency's movement against the USD.

DAC deflators are the OECD DAC's own deflators for converting ODA to constant prices. They combine donor-country inflation with exchange-rate movements against the USD, so an earlier year can be adjusted down as well as up. Japan's deflator, for example, falls from 136 in 2013 to 100 in 2024 (base 2024), so its 2013 ODA is lower in constant 2024 prices than in current prices. Consumer price indices and GDP deflators are not designed for ODA data and produce figures that cannot be compared with published OECD data.

A trend analysis covers multiple years of a topic or measure. A ranking analysis concerns the relative ordering of a measure within a single year.

Choosing a price basis

Constant prices suit trend analysis, because current-price figures for different years reflect different price levels and exchange rates. ONE's usual choice for trends is constant prices with the latest year in the OECD data as base year. An earlier base year can be useful, for example to match an existing publication, but makes recent figures differ from those in current publications.

Current prices suit single-year rankings, because they give the most accurate picture of relative size in that year. Constant prices with a base year other than the year of analysis can shift a ranking.

An analysis that combines a trend and a ranking can use constant prices for the trend and current prices for the ranking. Its ODA totals then differ between the two outputs because they use different price bases.

Pitfalls

• Mixing current and constant prices in the same chart or table is an error. Where a document needs both, each output carries its own label and a note explains the difference.
• "Constant prices" without a base year is ambiguous and makes figures unreproducible.
• In years with high inflation or large exchange-rate movements, donor rankings can change with the price basis.
• Figures compared with a published OECD source differ when the source uses another price basis or base year. The direction of the difference depends on each donor's inflation and exchange rate, so it can vary across donors.

What makes a result verifiable

A result is verifiable when it states the price basis of each component, the base year of any constant-price figure, and the deflator used, and explains why totals differ where components use different price bases.