| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 1 |
0.3%
|
| 1855 | 1 |
0.3%
|
|
| 1909 | 1 |
0.3%
|
|
| 1920 | 1 |
0.3%
|
|
| 1927 | 1 |
0.3%
|
|
| 1951 | 3 |
0.8%
|
|
| 1953 | 2 |
0.6%
|
|
| 1955 | 1 |
0.3%
|
|
| 1956 | 1 |
0.3%
|
|
| 1958 | 4 |
1.1%
|
|
| 1959 | 1 |
0.3%
|
|
| 1960 | 1 |
0.3%
|
|
| 1961 | 3 |
0.8%
|
|
| 1962 | 2 |
0.6%
|
|
| 1963 | 3 |
0.8%
|
|
| 1966 | 1 |
0.3%
|
|
| 1974 | 1 |
0.3%
|
|
| 1977 | 2 |
0.6%
|
|
| 1980 | 2 |
0.6%
|
|
| 1981 | 1 |
0.3%
|
|
| 1982 | 1 |
0.3%
|
|
| 1983 | 1 |
0.3%
|
|
| 1984 | 1 |
0.3%
|
|
| 1987 | 3 |
0.8%
|
|
| 1988 | 2 |
0.6%
|
|
| 1989 | 4 |
1.1%
|
|
| 1990 | 22 |
6.1%
|
|
| 1991 | 19 |
5.3%
|
|
| 1992 | 24 |
6.6%
|
|
| 1993 | 18 |
5%
|
|
| 1994 | 9 |
2.5%
|
|
| 1995 | 7 |
1.9%
|
|
| 1996 | 13 |
3.6%
|
|
| 1997 | 11 |
3%
|
|
| 1998 | 10 |
2.8%
|
|
| 1999 | 8 |
2.2%
|
|
| 2000 | 13 |
3.6%
|
|
| 2001 | 8 |
2.2%
|
|
| 2002 | 13 |
3.6%
|
|
| 2003 | 11 |
3%
|
|
| 2004 | 9 |
2.5%
|
|
| 2005 | 12 |
3.3%
|
|
| 2006 | 9 |
2.5%
|
|
| 2007 | 19 |
5.3%
|
|
| 2008 | 7 |
1.9%
|
|
| 2009 | 9 |
2.5%
|
|
| 2010 | 13 |
3.6%
|
|
| 2011 | 14 |
3.9%
|
|
| 2012 | 8 |
2.2%
|
|
| 2013 | 8 |
2.2%
|
|
| 2014 | 5 |
1.4%
|
|
| 2015 | 8 |
2.2%
|
|
| 2016 | 3 |
0.8%
|
|
| 2017 | 6 |
1.7%
|