Table 1.

Sample size at each timepoint between 1990–2007. N refers to the number of respondents. Note that newly enrolled students at the invited schools were invited to participate during the first waves of the study which increased the total sample size to at least 1242 unique individuals who have participated once

Year	1990	1991	1992	1993	1995	1996	1998	2000	2007
Age	13	14	15	16	18	19	21	23	30
N	924	958	963	789	779	643	634	627	536