| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 11 |
6.4%
|
| 1991 | 2 |
1.2%
|
|
| 1992 | 6 |
3.5%
|
|
| 1993 | 2 |
1.2%
|
|
| 1994 | 5 |
2.9%
|
|
| 1995 | 9 |
5.3%
|
|
| 1996 | 4 |
2.3%
|
|
| 1997 | 7 |
4.1%
|
|
| 1998 | 3 |
1.8%
|
|
| 1999 | 6 |
3.5%
|
|
| 2000 | 10 |
5.8%
|
|
| 2001 | 5 |
2.9%
|
|
| 2002 | 5 |
2.9%
|
|
| 2003 | 5 |
2.9%
|
|
| 2004 | 5 |
2.9%
|
|
| 2005 | 13 |
7.6%
|
|
| 2006 | 8 |
4.7%
|
|
| 2007 | 4 |
2.3%
|
|
| 2008 | 12 |
7%
|
|
| 2009 | 11 |
6.4%
|
|
| 2010 | 6 |
3.5%
|
|
| 2011 | 6 |
3.5%
|
|
| 2012 | 2 |
1.2%
|
|
| 2013 | 4 |
2.3%
|
|
| 2014 | 6 |
3.5%
|
|
| 2015 | 3 |
1.8%
|
|
| 2016 | 3 |
1.8%
|
|
| 2017 | 6 |
3.5%
|
|
| 2018 | 2 |
1.2%
|
|
| Sysmiss | 188 |