Country | Year of study | No. of study groups | Number of study participants | Age of children (years) |
Great Britain | 1980-1990 | 3 | 20 - 50 | 0 - 11 |
Netherlands | 1980-1990 | 1 | 50 - 209 | 0 - 17 |
Germany | 19911 | 1 | 13 | 0 - 1 |
USA | 19911 | 3 | 39 - 404 | 0 - 12 |
Slovakia | 19971 | 11 | 26 - 32 | 11 - 15 |
Belgium | 19991 | 1 | 38 | 6 - 17 |
Poland | 2003-2011 | 5 | 2 - 50 | 2 - 18 |