Table 1. Response rate.

	Response rate (%) School/Classes/Student
Survey year	2001/2002	2005/2006	2009/2010
Norway	73/88/89	69/69/84	55/56/81
Denmark	88/96/91	80/94/89	53/92/86
Finland	89/89/92	95/95/88	90/90/94
Sweden	84/84/87	83/83/85	88/88/77