"Only countries with data from (almost) all periods were included, the numbers of countries are given in parentheses. North: Norway, Sweden, Finland and Iceland. Western: Austria, Denmark, England & Wales, the Netherlands, Germany, Switzerland, Luxembourg and Ireland. Southern: Greece, Spain and Portugal. East: Estonia, Hungary and Poland. South Eastern: Bulgaria and Turkey. The percentages have been weighted with country population when calculating the group values." (Quoted from site)