| Value | Category | Cases | |
|---|---|---|---|
| 1979 | 31 |
1.1%
|
|
| 1988 | 7 |
0.2%
|
|
| 1990 | 33 |
1.2%
|
|
| 1997 | 2746 |
97.5%
|
|
| Sysmiss | 3788 |