| Value | Category | Cases | |
|---|---|---|---|
| 1 | mandatory | 236 |
4%
|
| 2 | voluntary | 976 |
16.6%
|
| 3 | both | 17 |
0.3%
|
| 4 | none | 4659 |
79.1%
|
| Sysmiss | 597 |