This note describes the situation for compiling aggregates in the Main Economic Indicators (MEI) database. Aggregates in the MEI are, wherever possible, always the latest composition (unless stated otherwise in the accompanying notes to the subject area) and include:

• OECD: all OECD countries
• OECD-Europe: all European countries that are members of the OECD
• EUU: all European Union Member States
• G7: the major seven economies of the OECD - the United States, Canada, Japan, France, Italy, Germany and the United Kingdom
• Euro area: all European Union Member States in the euro area

Aggregates are available for the following subjects: Industrial Production; Manufacturing; Construction; Permits Issued for Dwellings; Composite Leading Indicators; Confidence Indicators; Passenger Cars; Retail Trade; Price Indices; Hourly Earnings, Labour Statistics; Monetary Aggregates; Balance of Payments; and International Trade. The OECD compiles OECD, OECD-Europe and G7 aggregates, whereas aggregates for the European Union and Euro area are provided by the relevant European authorities (namely Eurostat or the European Central Bank).

Country coverage and length of time series
The MEI database aims to provide as long a time series as possible for aggregates, which requires long country time series for each subject. However, a special case exists for transition economies (the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia and Slovenia), where a cut-off has been set at 1990 for these country's contributions to aggregates. In fact, for many subjects, data may only be available from 1995 onwards for these countries. Aggregates which go further back than these dates therefore will not include the countries listed. In all cases the online subject metadata will provide full details.

In practice, the time series length and country composition of each aggregate will differ by subject depending on the length of time series available for countries and whether the relevant series (or a close proxy) exists. Estimations are performed by the secretariat, in a small number of cases, to ensure the above principles are adhered to as best as possible and to enable long time series to be produced for each subject.

Weights used for aggregates
The weights used to combine country data in forming aggregates differ depending on the subject. For example, Industrial Production, Composite Leading Indicators, Retail Trade, Hourly Earnings, Consumer Price Indices, Producer Price Indices and Monetary Aggregates all use relevant weights for the most recently available year (e.g. GDP) adjusted by Purchasing Power Parities. Other subject aggregates, for example Labour Statistics, Balance of Payments and International Trade are simply based on the sum of contributing countries data.

Where weights are used, aggregates use a chain-linked Laspeyres methodology. In most cases these are annually re-weighted chained Laspeyres indices, however for some subjects the series are chain-linked every five years when new weights are introduced, coinciding with the introduction of the OECD reference year.