| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 10 |
30.3%
|
| 2009 | 1 |
3%
|
|
| 2010 | 1 |
3%
|
|
| 2015 | 1 |
3%
|
|
| 2017 | 7 |
21.2%
|
|
| 2018 | 10 |
30.3%
|
|
| 2019 | 3 |
9.1%
|
|
| Sysmiss | 116 |