| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 6 |
1.7%
|
| 1952 | 1 |
0.3%
|
|
| 1959 | 1 |
0.3%
|
|
| 1961 | 1 |
0.3%
|
|
| 1989 | 1 |
0.3%
|
|
| 1990 | 2 |
0.6%
|
|
| 1991 | 21 |
5.8%
|
|
| 1992 | 23 |
6.4%
|
|
| 1993 | 32 |
8.9%
|
|
| 1994 | 21 |
5.8%
|
|
| 1995 | 16 |
4.5%
|
|
| 1996 | 10 |
2.8%
|
|
| 1997 | 15 |
4.2%
|
|
| 1998 | 13 |
3.6%
|
|
| 1999 | 11 |
3.1%
|
|
| 2000 | 15 |
4.2%
|
|
| 2001 | 14 |
3.9%
|
|
| 2002 | 9 |
2.5%
|
|
| 2003 | 19 |
5.3%
|
|
| 2004 | 10 |
2.8%
|
|
| 2005 | 19 |
5.3%
|
|
| 2006 | 11 |
3.1%
|
|
| 2007 | 10 |
2.8%
|
|
| 2008 | 11 |
3.1%
|
|
| 2009 | 9 |
2.5%
|
|
| 2010 | 11 |
3.1%
|
|
| 2011 | 8 |
2.2%
|
|
| 2012 | 8 |
2.2%
|
|
| 2013 | 11 |
3.1%
|
|
| 2014 | 4 |
1.1%
|
|
| 2015 | 8 |
2.2%
|
|
| 2016 | 7 |
1.9%
|
|
| 2017 | 1 |
0.3%
|