| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 0 |
0%
|
| 1927 | 1 |
0.6%
|
|
| 1935 | 1 |
0.6%
|
|
| 1950 | 1 |
0.6%
|
|
| 1960 | 1 |
0.6%
|
|
| 1967 | 1 |
0.6%
|
|
| 1973 | 1 |
0.6%
|
|
| 1978 | 1 |
0.6%
|
|
| 1982 | 1 |
0.6%
|
|
| 1983 | 1 |
0.6%
|
|
| 1987 | 1 |
0.6%
|
|
| 1990 | 1 |
0.6%
|
|
| 1991 | 2 |
1.2%
|
|
| 1992 | 2 |
1.2%
|
|
| 1993 | 2 |
1.2%
|
|
| 1994 | 1 |
0.6%
|
|
| 1995 | 2 |
1.2%
|
|
| 1996 | 4 |
2.5%
|
|
| 1997 | 6 |
3.7%
|
|
| 1998 | 6 |
3.7%
|
|
| 1999 | 3 |
1.8%
|
|
| 2000 | 15 |
9.2%
|
|
| 2001 | 5 |
3.1%
|
|
| 2002 | 4 |
2.5%
|
|
| 2003 | 6 |
3.7%
|
|
| 2004 | 9 |
5.5%
|
|
| 2005 | 4 |
2.5%
|
|
| 2006 | 9 |
5.5%
|
|
| 2007 | 2 |
1.2%
|
|
| 2008 | 4 |
2.5%
|
|
| 2009 | 6 |
3.7%
|
|
| 2010 | 7 |
4.3%
|
|
| 2011 | 4 |
2.5%
|
|
| 2012 | 5 |
3.1%
|
|
| 2013 | 6 |
3.7%
|
|
| 2014 | 7 |
4.3%
|
|
| 2015 | 9 |
5.5%
|
|
| 2016 | 7 |
4.3%
|
|
| 2017 | 4 |
2.5%
|
|
| 2018 | 6 |
3.7%
|
|
| 2019 | 1 |
0.6%
|
|
| 2020 | 3 |
1.8%
|
|
| 2022 | 1 |
0.6%
|