Age range and number of subjects who participated in each follow up survey
| 1st | 2nd | 3rd | 4th | 5th | 6th | 7th | |
|---|---|---|---|---|---|---|---|
| Year of survey | 1982 | 1984 | 1986 | 1988 | 1990 | 1992 | 1995–1997 |
| Age range of subjects (years) | 8–10 | 10–12 | 12–14 | 14–16 | 16–18 | 18–20 | 23–27 |
| Number of subjects who participated | 718 | 507 | 478 | 401 | 449 | 407 | 401 |