| Value | Category | Cases | |
|---|---|---|---|
| 1998 | 1 |
3%
|
|
| 2004 | 1 |
3%
|
|
| 2006 | 1 |
3%
|
|
| 2007 | 2 |
6.1%
|
|
| 9997 | Inconsistent | 0 |
0%
|
| 9999 | Missing | 28 |
84.8%
|
| Sysmiss | 1424 |