| Value | Category | Cases | |
|---|---|---|---|
| 1990 | 1 |
0.2%
|
|
| 1991 | 1 |
0.2%
|
|
| 1992 | 2 |
0.3%
|
|
| 1993 | 3 |
0.5%
|
|
| 1994 | 2 |
0.3%
|
|
| 1996 | 6 |
1%
|
|
| 1997 | 562 |
97.4%
|
|
| Sysmiss | 344 |