| Value | Category | Cases | |
|---|---|---|---|
| 1993 | 2 |
0.3%
|
|
| 2000 | 7 |
0.9%
|
|
| 2004 | 3 |
0.4%
|
|
| 2005 | 1 |
0.1%
|
|
| 2006 | 14 |
1.9%
|
|
| 2007 | 12 |
1.6%
|
|
| 2008 | 36 |
4.8%
|
|
| 2009 | 505 |
67.2%
|
|
| 2010 | 55 |
7.3%
|
|
| 9999 | never back | 117 |
15.6%
|
| Sysmiss | 25201 |