| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 0 |
0%
|
| 1906 | 1 |
0.3%
|
|
| 1920 | 1 |
0.3%
|
|
| 1921 | 1 |
0.3%
|
|
| 1934 | 2 |
0.6%
|
|
| 1935 | 1 |
0.3%
|
|
| 1939 | 1 |
0.3%
|
|
| 1940 | 1 |
0.3%
|
|
| 1942 | 1 |
0.3%
|
|
| 1945 | 1 |
0.3%
|
|
| 1958 | 2 |
0.6%
|
|
| 1959 | 1 |
0.3%
|
|
| 1962 | 3 |
0.9%
|
|
| 1963 | 1 |
0.3%
|
|
| 1964 | 1 |
0.3%
|
|
| 1965 | 1 |
0.3%
|
|
| 1966 | 1 |
0.3%
|
|
| 1967 | 1 |
0.3%
|
|
| 1968 | 2 |
0.6%
|
|
| 1969 | 2 |
0.6%
|
|
| 1970 | 5 |
1.4%
|
|
| 1971 | 1 |
0.3%
|
|
| 1972 | 5 |
1.4%
|
|
| 1973 | 1 |
0.3%
|
|
| 1974 | 1 |
0.3%
|
|
| 1975 | 1 |
0.3%
|
|
| 1976 | 3 |
0.9%
|
|
| 1977 | 4 |
1.2%
|
|
| 1978 | 1 |
0.3%
|
|
| 1980 | 4 |
1.2%
|
|
| 1981 | 3 |
0.9%
|
|
| 1982 | 4 |
1.2%
|
|
| 1983 | 1 |
0.3%
|
|
| 1984 | 3 |
0.9%
|
|
| 1985 | 7 |
2%
|
|
| 1986 | 1 |
0.3%
|
|
| 1987 | 3 |
0.9%
|
|
| 1988 | 4 |
1.2%
|
|
| 1989 | 5 |
1.4%
|
|
| 1990 | 1 |
0.3%
|
|
| 1991 | 1 |
0.3%
|
|
| 1992 | 11 |
3.2%
|
|
| 1993 | 7 |
2%
|
|
| 1994 | 6 |
1.7%
|
|
| 1995 | 7 |
2%
|
|
| 1996 | 5 |
1.4%
|
|
| 1997 | 5 |
1.4%
|
|
| 1998 | 10 |
2.9%
|
|
| 1999 | 11 |
3.2%
|
|
| 2000 | 13 |
3.8%
|
|
| 2001 | 10 |
2.9%
|
|
| 2002 | 8 |
2.3%
|
|
| 2003 | 16 |
4.6%
|
|
| 2004 | 6 |
1.7%
|
|
| 2005 | 12 |
3.5%
|
|
| 2006 | 9 |
2.6%
|
|
| 2007 | 20 |
5.8%
|
|
| 2008 | 5 |
1.4%
|
|
| 2009 | 7 |
2%
|
|
| 2010 | 7 |
2%
|
|
| 2011 | 8 |
2.3%
|
|
| 2012 | 8 |
2.3%
|
|
| 2013 | 12 |
3.5%
|
|
| 2014 | 12 |
3.5%
|
|
| 2015 | 8 |
2.3%
|
|
| 2016 | 7 |
2%
|
|
| 2017 | 12 |
3.5%
|
|
| 2018 | 9 |
2.6%
|
|
| 2019 | 4 |
1.2%
|
|
| 2020 | 4 |
1.2%
|
|
| 2021 | 2 |
0.6%
|