| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 1 |
0.1%
|
| 1947 | 1 |
0.1%
|
|
| 1957 | 1 |
0.1%
|
|
| 1960 | 1 |
0.1%
|
|
| 1962 | 3 |
0.4%
|
|
| 1965 | 2 |
0.3%
|
|
| 1968 | 3 |
0.4%
|
|
| 1969 | 1 |
0.1%
|
|
| 1970 | 1 |
0.1%
|
|
| 1972 | 1 |
0.1%
|
|
| 1982 | 1 |
0.1%
|
|
| 1987 | 1 |
0.1%
|
|
| 1989 | 3 |
0.4%
|
|
| 1990 | 20 |
2.8%
|
|
| 1991 | 28 |
3.9%
|
|
| 1992 | 13 |
1.8%
|
|
| 1993 | 22 |
3.1%
|
|
| 1994 | 27 |
3.8%
|
|
| 1995 | 14 |
2%
|
|
| 1996 | 17 |
2.4%
|
|
| 1997 | 25 |
3.5%
|
|
| 1998 | 27 |
3.8%
|
|
| 1999 | 26 |
3.7%
|
|
| 2000 | 18 |
2.5%
|
|
| 2001 | 18 |
2.5%
|
|
| 2002 | 21 |
3%
|
|
| 2003 | 29 |
4.1%
|
|
| 2004 | 27 |
3.8%
|
|
| 2005 | 42 |
5.9%
|
|
| 2006 | 18 |
2.5%
|
|
| 2007 | 38 |
5.4%
|
|
| 2008 | 25 |
3.5%
|
|
| 2009 | 22 |
3.1%
|
|
| 2010 | 19 |
2.7%
|
|
| 2011 | 16 |
2.3%
|
|
| 2012 | 15 |
2.1%
|
|
| 2013 | 26 |
3.7%
|
|
| 2014 | 23 |
3.2%
|
|
| 2015 | 20 |
2.8%
|
|
| 2016 | 21 |
3%
|
|
| 2017 | 20 |
2.8%
|
|
| 2018 | 16 |
2.3%
|
|
| 2019 | 21 |
3%
|
|
| 2020 | 11 |
1.5%
|
|
| 2021 | 4 |
0.6%
|
|
| 2022 | 1 |
0.1%
|