| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 20 |
1.5%
|
| 1880 | 1 |
0.1%
|
|
| 1896 | 1 |
0.1%
|
|
| 1911 | 2 |
0.1%
|
|
| 1912 | 1 |
0.1%
|
|
| 1927 | 1 |
0.1%
|
|
| 1928 | 3 |
0.2%
|
|
| 1929 | 1 |
0.1%
|
|
| 1930 | 2 |
0.1%
|
|
| 1932 | 1 |
0.1%
|
|
| 1933 | 1 |
0.1%
|
|
| 1934 | 3 |
0.2%
|
|
| 1935 | 3 |
0.2%
|
|
| 1936 | 5 |
0.4%
|
|
| 1937 | 1 |
0.1%
|
|
| 1940 | 1 |
0.1%
|
|
| 1943 | 2 |
0.1%
|
|
| 1944 | 1 |
0.1%
|
|
| 1945 | 3 |
0.2%
|
|
| 1946 | 7 |
0.5%
|
|
| 1947 | 3 |
0.2%
|
|
| 1949 | 1 |
0.1%
|
|
| 1951 | 1 |
0.1%
|
|
| 1952 | 3 |
0.2%
|
|
| 1954 | 2 |
0.1%
|
|
| 1955 | 3 |
0.2%
|
|
| 1956 | 6 |
0.4%
|
|
| 1957 | 2 |
0.1%
|
|
| 1958 | 4 |
0.3%
|
|
| 1959 | 1 |
0.1%
|
|
| 1960 | 1 |
0.1%
|
|
| 1961 | 2 |
0.1%
|
|
| 1962 | 2 |
0.1%
|
|
| 1963 | 2 |
0.1%
|
|
| 1964 | 5 |
0.4%
|
|
| 1965 | 3 |
0.2%
|
|
| 1966 | 3 |
0.2%
|
|
| 1967 | 2 |
0.1%
|
|
| 1968 | 1 |
0.1%
|
|
| 1969 | 1 |
0.1%
|
|
| 1970 | 1 |
0.1%
|
|
| 1971 | 2 |
0.1%
|
|
| 1972 | 5 |
0.4%
|
|
| 1973 | 3 |
0.2%
|
|
| 1974 | 1 |
0.1%
|
|
| 1975 | 2 |
0.1%
|
|
| 1976 | 3 |
0.2%
|
|
| 1978 | 3 |
0.2%
|
|
| 1980 | 4 |
0.3%
|
|
| 1982 | 2 |
0.1%
|
|
| 1983 | 2 |
0.1%
|
|
| 1984 | 1 |
0.1%
|
|
| 1986 | 2 |
0.1%
|
|
| 1988 | 2 |
0.1%
|
|
| 1989 | 8 |
0.6%
|
|
| 1990 | 8 |
0.6%
|
|
| 1991 | 32 |
2.4%
|
|
| 1992 | 47 |
3.5%
|
|
| 1993 | 40 |
3%
|
|
| 1994 | 58 |
4.3%
|
|
| 1995 | 68 |
5.1%
|
|
| 1996 | 76 |
5.7%
|
|
| 1997 | 62 |
4.6%
|
|
| 1998 | 72 |
5.4%
|
|
| 1999 | 51 |
3.8%
|
|
| 2000 | 65 |
4.9%
|
|
| 2001 | 58 |
4.3%
|
|
| 2002 | 43 |
3.2%
|
|
| 2003 | 65 |
4.9%
|
|
| 2004 | 50 |
3.7%
|
|
| 2005 | 50 |
3.7%
|
|
| 2006 | 55 |
4.1%
|
|
| 2007 | 50 |
3.7%
|
|
| 2008 | 39 |
2.9%
|
|
| 2009 | 35 |
2.6%
|
|
| 2010 | 45 |
3.4%
|
|
| 2011 | 36 |
2.7%
|
|
| 2012 | 33 |
2.5%
|
|
| 2013 | 32 |
2.4%
|
|
| 2014 | 11 |
0.8%
|
|
| 2015 | 2 |
0.1%
|
|
| 2016 | 2 |
0.1%
|
|
| 2017 | 3 |
0.2%
|