Table 1.
Sample characteristics. Years 2000-2010
| Characteristic | 2000 | 2001 | 2002 | 2003 | 2004 | 2005 | 2006 | 2007 | 2008 | 2009 | 2010 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| N |
22,418 |
22,257 |
15,752 |
25,299 |
32,372 |
41,365 |
38,748 |
40,407 |
38,681 |
32,461 |
25,555 |
| Age (mean±SD) |
17.1 ± 1.5 |
17.1 ± 1.4 |
17.2 ± 1.6 |
17.1 ± 1.6 |
17.1 ± 1.6 |
17.1 ± 1.6 |
17.1 ± 1.6 |
17.1 ± 1.6 |
17.2 ± 1.6 |
17.1 ± 1.6 |
17.1 ± 1.4 |
| Gender (male) |
47.3% |
45.0% |
45.5% |
45.5% |
48.1% |
48.1% |
48.9% |
49.7% |
49.0% |
49.2% |
47.9% |
| Response rate* | 100.0% | 87.1% | 98.6% | 94.9% | 96.1% | 94.1% | 88.9% | 92.4% | 85.8% | 89.2% | 86.2% |
* Response rate of schools participating in the survey; SD = Standard Deviation.