| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 0 |
0%
|
| 1989 | 1 |
1.4%
|
|
| 1995 | 1 |
1.4%
|
|
| 1998 | 1 |
1.4%
|
|
| 1999 | 1 |
1.4%
|
|
| 2000 | 5 |
6.9%
|
|
| 2001 | 1 |
1.4%
|
|
| 2004 | 1 |
1.4%
|
|
| 2005 | 4 |
5.6%
|
|
| 2006 | 1 |
1.4%
|
|
| 2007 | 3 |
4.2%
|
|
| 2008 | 4 |
5.6%
|
|
| 2009 | 3 |
4.2%
|
|
| 2010 | 8 |
11.1%
|
|
| 2011 | 3 |
4.2%
|
|
| 2012 | 6 |
8.3%
|
|
| 2013 | 9 |
12.5%
|
|
| 2014 | 4 |
5.6%
|
|
| 2015 | 11 |
15.3%
|
|
| 2016 | 3 |
4.2%
|
|
| 2017 | 2 |
2.8%
|
|
| Sysmiss | 39 |