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