| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 9 |
6%
|
| 1970 | 2 |
1.3%
|
|
| 1973 | 1 |
0.7%
|
|
| 1975 | 1 |
0.7%
|
|
| 1982 | 1 |
0.7%
|
|
| 1984 | 1 |
0.7%
|
|
| 1986 | 1 |
0.7%
|
|
| 1988 | 2 |
1.3%
|
|
| 1989 | 2 |
1.3%
|
|
| 1990 | 1 |
0.7%
|
|
| 1991 | 2 |
1.3%
|
|
| 1992 | 2 |
1.3%
|
|
| 1993 | 2 |
1.3%
|
|
| 1994 | 2 |
1.3%
|
|
| 1995 | 4 |
2.6%
|
|
| 1996 | 1 |
0.7%
|
|
| 1997 | 4 |
2.6%
|
|
| 1998 | 8 |
5.3%
|
|
| 1999 | 3 |
2%
|
|
| 2000 | 4 |
2.6%
|
|
| 2001 | 2 |
1.3%
|
|
| 2002 | 7 |
4.6%
|
|
| 2003 | 3 |
2%
|
|
| 2004 | 7 |
4.6%
|
|
| 2005 | 10 |
6.6%
|
|
| 2006 | 3 |
2%
|
|
| 2007 | 9 |
6%
|
|
| 2008 | 5 |
3.3%
|
|
| 2009 | 9 |
6%
|
|
| 2010 | 10 |
6.6%
|
|
| 2011 | 3 |
2%
|
|
| 2012 | 5 |
3.3%
|
|
| 2013 | 5 |
3.3%
|
|
| 2014 | 12 |
7.9%
|
|
| 2016 | 3 |
2%
|
|
| 2017 | 5 |
3.3%
|