Various mean values are given in the OECD statistics. These take into account the OECD countries for which data are available or can be estimated. The value for the “OECD average” is calculated as the unweighted mean of the data values for all OECD countries. “Total OECD” is calculated as the weighted mean of the data values of all OECD countries.
The “EU average” is calculated as the unweighted mean of the data values of the OECD countries that are members or accession countries of both the European Union and the OECD for which data are available or can be estimated. For the description of the various EU averages, refer to the glossary term "EU – European Union."
For more information on which countries were included in the calculation of the international averages in the individual reporting years, see source.
(Source: OECD, Education at a Glance)