| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 1 |
0.2%
|
| 1887 | 1 |
0.2%
|
|
| 1928 | 1 |
0.2%
|
|
| 1956 | 1 |
0.2%
|
|
| 1965 | 1 |
0.2%
|
|
| 1969 | 2 |
0.3%
|
|
| 1970 | 1 |
0.2%
|
|
| 1987 | 1 |
0.2%
|
|
| 1988 | 1 |
0.2%
|
|
| 1989 | 3 |
0.5%
|
|
| 1990 | 2 |
0.3%
|
|
| 1991 | 1 |
0.2%
|
|
| 1992 | 5 |
0.9%
|
|
| 1993 | 4 |
0.7%
|
|
| 1994 | 6 |
1%
|
|
| 1995 | 12 |
2.1%
|
|
| 1996 | 19 |
3.3%
|
|
| 1997 | 14 |
2.4%
|
|
| 1998 | 11 |
1.9%
|
|
| 1999 | 8 |
1.4%
|
|
| 2000 | 11 |
1.9%
|
|
| 2001 | 14 |
2.4%
|
|
| 2002 | 12 |
2.1%
|
|
| 2003 | 10 |
1.7%
|
|
| 2004 | 17 |
2.9%
|
|
| 2005 | 19 |
3.3%
|
|
| 2006 | 23 |
4%
|
|
| 2007 | 23 |
4%
|
|
| 2008 | 35 |
6%
|
|
| 2009 | 26 |
4.5%
|
|
| 2010 | 29 |
5%
|
|
| 2011 | 33 |
5.7%
|
|
| 2012 | 37 |
6.4%
|
|
| 2013 | 31 |
5.3%
|
|
| 2014 | 29 |
5%
|
|
| 2015 | 38 |
6.5%
|
|
| 2016 | 45 |
7.7%
|
|
| 2017 | 34 |
5.9%
|
|
| 2018 | 20 |
3.4%
|