| Value | Category | Cases | |
|---|---|---|---|
| -2 | Refusal to answer | 0 |
0%
|
| -1 | Don't know | 2 |
10%
|
| 1997 | 1 |
5%
|
|
| 1999 | 2 |
10%
|
|
| 2000 | 4 |
20%
|
|
| 2001 | 11 |
55%
|
|
| Sysmiss | 7829 |