| Value | Category | Cases | |
|---|---|---|---|
| 1991 | 1 |
0.6%
|
|
| 1996 | 36 |
21.4%
|
|
| 1997 | 59 |
35.1%
|
|
| 1998 | 55 |
32.7%
|
|
| 1999 | 17 |
10.1%
|
|
| Sysmiss | 4257 |