| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 0 |
0%
|
| 1907 | 1 |
0.3%
|
|
| 1918 | 1 |
0.3%
|
|
| 1929 | 1 |
0.3%
|
|
| 1944 | 2 |
0.6%
|
|
| 1945 | 1 |
0.3%
|
|
| 1946 | 1 |
0.3%
|
|
| 1950 | 1 |
0.3%
|
|
| 1952 | 1 |
0.3%
|
|
| 1955 | 3 |
0.8%
|
|
| 1961 | 1 |
0.3%
|
|
| 1965 | 1 |
0.3%
|
|
| 1967 | 1 |
0.3%
|
|
| 1980 | 1 |
0.3%
|
|
| 1984 | 1 |
0.3%
|
|
| 1989 | 1 |
0.3%
|
|
| 1990 | 1 |
0.3%
|
|
| 1991 | 17 |
4.7%
|
|
| 1992 | 24 |
6.7%
|
|
| 1993 | 17 |
4.7%
|
|
| 1994 | 18 |
5%
|
|
| 1995 | 17 |
4.7%
|
|
| 1996 | 15 |
4.2%
|
|
| 1997 | 23 |
6.4%
|
|
| 1998 | 14 |
3.9%
|
|
| 1999 | 11 |
3.1%
|
|
| 2000 | 11 |
3.1%
|
|
| 2001 | 12 |
3.4%
|
|
| 2002 | 12 |
3.4%
|
|
| 2003 | 16 |
4.5%
|
|
| 2004 | 13 |
3.6%
|
|
| 2005 | 9 |
2.5%
|
|
| 2006 | 11 |
3.1%
|
|
| 2007 | 9 |
2.5%
|
|
| 2008 | 11 |
3.1%
|
|
| 2009 | 11 |
3.1%
|
|
| 2010 | 15 |
4.2%
|
|
| 2011 | 12 |
3.4%
|
|
| 2012 | 7 |
2%
|
|
| 2013 | 8 |
2.2%
|
|
| 2014 | 10 |
2.8%
|
|
| 2015 | 9 |
2.5%
|
|
| 2016 | 6 |
1.7%
|
|
| 2017 | 1 |
0.3%
|