| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 66 |
26.4%
|
| 1954 | 1 |
0.4%
|
|
| 1970 | 2 |
0.8%
|
|
| 1997 | 1 |
0.4%
|
|
| 1999 | 1 |
0.4%
|
|
| 2000 | 8 |
3.2%
|
|
| 2001 | 2 |
0.8%
|
|
| 2002 | 8 |
3.2%
|
|
| 2003 | 11 |
4.4%
|
|
| 2004 | 9 |
3.6%
|
|
| 2005 | 6 |
2.4%
|
|
| 2006 | 11 |
4.4%
|
|
| 2007 | 10 |
4%
|
|
| 2008 | 11 |
4.4%
|
|
| 2009 | 5 |
2%
|
|
| 2010 | 21 |
8.4%
|
|
| 2011 | 8 |
3.2%
|
|
| 2012 | 12 |
4.8%
|
|
| 2013 | 11 |
4.4%
|
|
| 2014 | 7 |
2.8%
|
|
| 2015 | 17 |
6.8%
|
|
| 2016 | 10 |
4%
|
|
| 2017 | 8 |
3.2%
|
|
| 2018 | 4 |
1.6%
|
|
| Sysmiss | 1073 |