| Value | Category | Cases | |
|---|---|---|---|
| 1996 | 3 |
11.5%
|
|
| 1997 | 16 |
61.5%
|
|
| 1998 | 4 |
15.4%
|
|
| 1999 | 3 |
11.5%
|
|
| 9997 | inconsistent | 0 |
0%
|
| 9998 | dk | 0 |
0%
|
| Sysmiss | 6729 |