| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 4 |
16%
|
| 2017 | 5 |
20%
|
|
| 2018 | 6 |
24%
|
|
| 2019 | 6 |
24%
|
|
| 2020 | 4 |
16%
|
|
| Sysmiss | 935 |