| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 17 |
13.2%
|
| 2006 | 5 |
3.9%
|
|
| 2008 | 1 |
0.8%
|
|
| 2009 | 7 |
5.4%
|
|
| 2010 | 4 |
3.1%
|
|
| 2011 | 6 |
4.7%
|
|
| 2012 | 6 |
4.7%
|
|
| 2013 | 5 |
3.9%
|
|
| 2014 | 9 |
7%
|
|
| 2015 | 8 |
6.2%
|
|
| 2016 | 14 |
10.9%
|
|
| 2017 | 27 |
20.9%
|
|
| 2018 | 20 |
15.5%
|
|
| Sysmiss | 472 |