oecd_region returns a vector of region representing OECD. The
selection is based on the GDP of countries. If the total GDP of OECD
countries from the region is greater than 50% of total GDP of the region,
the region is considered as belonging of the OECD.
See also
Other misc functions:
brazil_regions(),
china_regions(),
eu27_regions(),
eu28_regions(),
eu_regions(),
europe_regions(),
india_regions(),
region_id(),
usa_regions()
