| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 5 |
4.1%
|
| 2000 | 1 |
0.8%
|
|
| 2007 | 2 |
1.6%
|
|
| 2008 | 3 |
2.5%
|
|
| 2011 | 1 |
0.8%
|
|
| 2013 | 3 |
2.5%
|
|
| 2014 | 1 |
0.8%
|
|
| 2015 | 5 |
4.1%
|
|
| 2016 | 16 |
13.1%
|
|
| 2017 | 27 |
22.1%
|
|
| 2018 | 58 |
47.5%
|
|
| Sysmiss | 236 |