| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 3 |
2.1%
|
| 1924 | 1 |
0.7%
|
|
| 1946 | 1 |
0.7%
|
|
| 1948 | 2 |
1.4%
|
|
| 1952 | 1 |
0.7%
|
|
| 1959 | 1 |
0.7%
|
|
| 1965 | 1 |
0.7%
|
|
| 1967 | 1 |
0.7%
|
|
| 1968 | 2 |
1.4%
|
|
| 1969 | 1 |
0.7%
|
|
| 1970 | 1 |
0.7%
|
|
| 1971 | 1 |
0.7%
|
|
| 1972 | 3 |
2.1%
|
|
| 1973 | 4 |
2.8%
|
|
| 1974 | 1 |
0.7%
|
|
| 1975 | 1 |
0.7%
|
|
| 1976 | 2 |
1.4%
|
|
| 1979 | 1 |
0.7%
|
|
| 1980 | 1 |
0.7%
|
|
| 1982 | 2 |
1.4%
|
|
| 1983 | 1 |
0.7%
|
|
| 1984 | 2 |
1.4%
|
|
| 1985 | 2 |
1.4%
|
|
| 1986 | 2 |
1.4%
|
|
| 1987 | 2 |
1.4%
|
|
| 1989 | 1 |
0.7%
|
|
| 1990 | 5 |
3.4%
|
|
| 1991 | 1 |
0.7%
|
|
| 1992 | 3 |
2.1%
|
|
| 1993 | 4 |
2.8%
|
|
| 1994 | 1 |
0.7%
|
|
| 1995 | 2 |
1.4%
|
|
| 1996 | 2 |
1.4%
|
|
| 1997 | 1 |
0.7%
|
|
| 1998 | 6 |
4.1%
|
|
| 1999 | 4 |
2.8%
|
|
| 2000 | 3 |
2.1%
|
|
| 2001 | 2 |
1.4%
|
|
| 2002 | 3 |
2.1%
|
|
| 2004 | 6 |
4.1%
|
|
| 2005 | 4 |
2.8%
|
|
| 2006 | 2 |
1.4%
|
|
| 2007 | 2 |
1.4%
|
|
| 2008 | 8 |
5.5%
|
|
| 2010 | 2 |
1.4%
|
|
| 2012 | 6 |
4.1%
|
|
| 2013 | 5 |
3.4%
|
|
| 2014 | 9 |
6.2%
|
|
| 2015 | 6 |
4.1%
|
|
| 2016 | 4 |
2.8%
|
|
| 2017 | 4 |
2.8%
|
|
| 2018 | 3 |
2.1%
|
|
| 2019 | 2 |
1.4%
|
|
| 2021 | 1 |
0.7%
|
|
| 2023 | 3 |
2.1%
|