The World Health Organization (WHO) definition of the European region has been considered to determine the countries to be included in the study.

Figure 1. The WHO European Region (available at http://www.euro.who.int/countryinformation)
As a result, the following 52 countries have been explored:
| Albania |
Czech Republic |
Israel |
Poland |
Sweden |
| Andorra |
Denmark |
Italy |
Portugal |
Switzerland |
| Armenia |
Estonia |
Kazakhstan |
Republic of Moldova |
Tajikistan |
| Austria |
Finland |
Kyrgyzstan |
Republic of Macedonia |
Turkey |
| Azerbaijan |
France |
Latvia |
Romania |
Turkmenistan |
| Belarus |
Georgia |
Lithuania |
Russian Federation |
Ukraine |
| Belgium |
Germany |
Luxembourg |
San Marino |
United Kingdom |
| Bosnia and Herzegovina |
Greece |
Malta |
Serbia and Montegro |
Uzbekistan |
| Bulgaria |
Hungary |
Monaco |
Slovakia |
|
| Croatia |
Iceland |
Netherlands |
Slovenia |
|
| Cyprus |
Ireland |
Norway |
Spain |
|