| Value | Category | Cases | |
|---|---|---|---|
| 1991 | 1 |
0.2%
|
|
| 1992 | 1 |
0.2%
|
|
| 1993 | 2 |
0.4%
|
|
| 1994 | 1 |
0.2%
|
|
| 1996 | 3 |
0.6%
|
|
| 1997 | 470 |
98.3%
|
|
| Sysmiss | 443 |