| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 0 |
0%
|
| 1893 | 1 |
0.1%
|
|
| 1907 | 1 |
0.1%
|
|
| 1926 | 2 |
0.3%
|
|
| 1936 | 2 |
0.3%
|
|
| 1942 | 1 |
0.1%
|
|
| 1947 | 1 |
0.1%
|
|
| 1951 | 1 |
0.1%
|
|
| 1954 | 1 |
0.1%
|
|
| 1955 | 1 |
0.1%
|
|
| 1960 | 2 |
0.3%
|
|
| 1962 | 1 |
0.1%
|
|
| 1964 | 2 |
0.3%
|
|
| 1965 | 1 |
0.1%
|
|
| 1966 | 2 |
0.3%
|
|
| 1967 | 3 |
0.4%
|
|
| 1968 | 2 |
0.3%
|
|
| 1971 | 2 |
0.3%
|
|
| 1974 | 3 |
0.4%
|
|
| 1975 | 3 |
0.4%
|
|
| 1976 | 1 |
0.1%
|
|
| 1977 | 2 |
0.3%
|
|
| 1979 | 1 |
0.1%
|
|
| 1987 | 2 |
0.3%
|
|
| 1988 | 2 |
0.3%
|
|
| 1989 | 8 |
1%
|
|
| 1990 | 14 |
1.8%
|
|
| 1991 | 26 |
3.4%
|
|
| 1992 | 34 |
4.4%
|
|
| 1993 | 19 |
2.5%
|
|
| 1994 | 28 |
3.6%
|
|
| 1995 | 21 |
2.7%
|
|
| 1996 | 28 |
3.6%
|
|
| 1997 | 26 |
3.4%
|
|
| 1998 | 24 |
3.1%
|
|
| 1999 | 26 |
3.4%
|
|
| 2000 | 18 |
2.3%
|
|
| 2001 | 22 |
2.8%
|
|
| 2002 | 31 |
4%
|
|
| 2003 | 27 |
3.5%
|
|
| 2004 | 31 |
4%
|
|
| 2005 | 24 |
3.1%
|
|
| 2006 | 19 |
2.5%
|
|
| 2007 | 27 |
3.5%
|
|
| 2008 | 91 |
11.8%
|
|
| 2009 | 42 |
5.4%
|
|
| 2010 | 40 |
5.2%
|
|
| 2011 | 17 |
2.2%
|
|
| 2012 | 15 |
1.9%
|
|
| 2013 | 32 |
4.1%
|
|
| 2014 | 10 |
1.3%
|
|
| 2015 | 14 |
1.8%
|
|
| 2016 | 14 |
1.8%
|
|
| 2017 | 4 |
0.5%
|