Table 1 Study characteristics of the three surveys
2002 | 2006 | 2010 | All | |||||
|---|---|---|---|---|---|---|---|---|
N | % | N | % | N | % | N | % | |
Gender | ||||||||
Girls | 2864 | 50.7 | 3606 | 49.6 | 2576 | 51.5 | 9046 | 50.5 |
Boys | 2786 | 49.3 | 3668 | 50.4 | 2429 | 48.5 | 8883 | 49.5 |
Age | ||||||||
11 | 2094 | 37.2 | 2231 | 30.9 | 1687 | 34.0 | 6012 | 33.7 |
13 | 1800 | 31.9 | 2441 | 33,8 | 1628 | 32.9 | 5869 | 32.9 |
15 | 1741 | 30.9 | 2552 | 35.3 | 1640 | 33.1 | 5933 | 33.3 |