| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 0 |
0%
|
| 1927 | 1 |
0.2%
|
|
| 1947 | 2 |
0.4%
|
|
| 1950 | 1 |
0.2%
|
|
| 1951 | 2 |
0.4%
|
|
| 1953 | 1 |
0.2%
|
|
| 1954 | 1 |
0.2%
|
|
| 1956 | 1 |
0.2%
|
|
| 1957 | 1 |
0.2%
|
|
| 1958 | 1 |
0.2%
|
|
| 1960 | 1 |
0.2%
|
|
| 1963 | 1 |
0.2%
|
|
| 1965 | 1 |
0.2%
|
|
| 1977 | 1 |
0.2%
|
|
| 1978 | 2 |
0.4%
|
|
| 1979 | 1 |
0.2%
|
|
| 1981 | 2 |
0.4%
|
|
| 1987 | 2 |
0.4%
|
|
| 1989 | 5 |
1%
|
|
| 1990 | 17 |
3.4%
|
|
| 1991 | 12 |
2.4%
|
|
| 1992 | 31 |
6.2%
|
|
| 1993 | 23 |
4.6%
|
|
| 1994 | 6 |
1.2%
|
|
| 1995 | 9 |
1.8%
|
|
| 1996 | 14 |
2.8%
|
|
| 1997 | 13 |
2.6%
|
|
| 1998 | 18 |
3.6%
|
|
| 1999 | 10 |
2%
|
|
| 2000 | 12 |
2.4%
|
|
| 2001 | 20 |
4%
|
|
| 2002 | 17 |
3.4%
|
|
| 2003 | 18 |
3.6%
|
|
| 2004 | 14 |
2.8%
|
|
| 2005 | 20 |
4%
|
|
| 2006 | 17 |
3.4%
|
|
| 2007 | 23 |
4.6%
|
|
| 2008 | 13 |
2.6%
|
|
| 2009 | 14 |
2.8%
|
|
| 2010 | 15 |
3%
|
|
| 2011 | 14 |
2.8%
|
|
| 2012 | 17 |
3.4%
|
|
| 2013 | 15 |
3%
|
|
| 2014 | 6 |
1.2%
|
|
| 2015 | 10 |
2%
|
|
| 2016 | 10 |
2%
|
|
| 2017 | 14 |
2.8%
|
|
| 2018 | 17 |
3.4%
|
|
| 2019 | 14 |
2.8%
|
|
| 2020 | 8 |
1.6%
|
|
| 2021 | 11 |
2.2%
|
|
| 2022 | 2 |
0.4%
|
|
| 2023 | 1 |
0.2%
|