| Value | Category | Cases | |
|---|---|---|---|
| 1978 | 31 |
1.1%
|
|
| 1984 | 7 |
0.2%
|
|
| 1986 | 1 |
0%
|
|
| 1988 | 52 |
1.8%
|
|
| 1992 | 16 |
0.6%
|
|
| 1997 | 2746 |
96.2%
|
|
| Sysmiss | 3752 |