| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 6 |
2.6%
|
| 1869 | 1 |
0.4%
|
|
| 1891 | 1 |
0.4%
|
|
| 1903 | 1 |
0.4%
|
|
| 1920 | 1 |
0.4%
|
|
| 1933 | 1 |
0.4%
|
|
| 1935 | 1 |
0.4%
|
|
| 1938 | 1 |
0.4%
|
|
| 1939 | 2 |
0.9%
|
|
| 1940 | 1 |
0.4%
|
|
| 1942 | 1 |
0.4%
|
|
| 1945 | 1 |
0.4%
|
|
| 1948 | 2 |
0.9%
|
|
| 1951 | 2 |
0.9%
|
|
| 1954 | 2 |
0.9%
|
|
| 1956 | 1 |
0.4%
|
|
| 1957 | 1 |
0.4%
|
|
| 1958 | 1 |
0.4%
|
|
| 1959 | 2 |
0.9%
|
|
| 1963 | 1 |
0.4%
|
|
| 1965 | 1 |
0.4%
|
|
| 1966 | 1 |
0.4%
|
|
| 1967 | 1 |
0.4%
|
|
| 1968 | 3 |
1.3%
|
|
| 1969 | 3 |
1.3%
|
|
| 1970 | 2 |
0.9%
|
|
| 1971 | 3 |
1.3%
|
|
| 1973 | 1 |
0.4%
|
|
| 1975 | 1 |
0.4%
|
|
| 1976 | 2 |
0.9%
|
|
| 1977 | 1 |
0.4%
|
|
| 1978 | 3 |
1.3%
|
|
| 1980 | 3 |
1.3%
|
|
| 1981 | 1 |
0.4%
|
|
| 1982 | 7 |
3%
|
|
| 1983 | 2 |
0.9%
|
|
| 1984 | 2 |
0.9%
|
|
| 1985 | 2 |
0.9%
|
|
| 1987 | 2 |
0.9%
|
|
| 1988 | 2 |
0.9%
|
|
| 1989 | 2 |
0.9%
|
|
| 1990 | 10 |
4.3%
|
|
| 1991 | 1 |
0.4%
|
|
| 1992 | 4 |
1.7%
|
|
| 1993 | 5 |
2.1%
|
|
| 1994 | 5 |
2.1%
|
|
| 1995 | 5 |
2.1%
|
|
| 1996 | 7 |
3%
|
|
| 1997 | 6 |
2.6%
|
|
| 1998 | 9 |
3.9%
|
|
| 1999 | 5 |
2.1%
|
|
| 2000 | 16 |
6.9%
|
|
| 2001 | 4 |
1.7%
|
|
| 2002 | 6 |
2.6%
|
|
| 2003 | 5 |
2.1%
|
|
| 2004 | 8 |
3.4%
|
|
| 2005 | 6 |
2.6%
|
|
| 2006 | 8 |
3.4%
|
|
| 2007 | 5 |
2.1%
|
|
| 2008 | 7 |
3%
|
|
| 2009 | 5 |
2.1%
|
|
| 2010 | 7 |
3%
|
|
| 2011 | 4 |
1.7%
|
|
| 2012 | 6 |
2.6%
|
|
| 2013 | 3 |
1.3%
|
|
| 2014 | 4 |
1.7%
|
|
| 2015 | 4 |
1.7%
|
|
| 2016 | 2 |
0.9%
|
|
| 2018 | 1 |
0.4%
|