| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 1 |
0.3%
|
| 1882 | 1 |
0.3%
|
|
| 1923 | 1 |
0.3%
|
|
| 1936 | 1 |
0.3%
|
|
| 1946 | 1 |
0.3%
|
|
| 1947 | 2 |
0.6%
|
|
| 1948 | 1 |
0.3%
|
|
| 1955 | 1 |
0.3%
|
|
| 1956 | 2 |
0.6%
|
|
| 1957 | 2 |
0.6%
|
|
| 1959 | 1 |
0.3%
|
|
| 1964 | 1 |
0.3%
|
|
| 1966 | 1 |
0.3%
|
|
| 1967 | 1 |
0.3%
|
|
| 1968 | 3 |
0.8%
|
|
| 1972 | 2 |
0.6%
|
|
| 1974 | 1 |
0.3%
|
|
| 1975 | 1 |
0.3%
|
|
| 1977 | 1 |
0.3%
|
|
| 1978 | 1 |
0.3%
|
|
| 1982 | 1 |
0.3%
|
|
| 1983 | 1 |
0.3%
|
|
| 1984 | 1 |
0.3%
|
|
| 1986 | 1 |
0.3%
|
|
| 1987 | 1 |
0.3%
|
|
| 1988 | 1 |
0.3%
|
|
| 1989 | 4 |
1.1%
|
|
| 1990 | 12 |
3.3%
|
|
| 1991 | 13 |
3.6%
|
|
| 1992 | 25 |
6.9%
|
|
| 1993 | 24 |
6.7%
|
|
| 1994 | 18 |
5%
|
|
| 1995 | 15 |
4.2%
|
|
| 1996 | 9 |
2.5%
|
|
| 1997 | 6 |
1.7%
|
|
| 1998 | 15 |
4.2%
|
|
| 1999 | 12 |
3.3%
|
|
| 2000 | 14 |
3.9%
|
|
| 2001 | 16 |
4.4%
|
|
| 2002 | 9 |
2.5%
|
|
| 2003 | 14 |
3.9%
|
|
| 2004 | 9 |
2.5%
|
|
| 2005 | 14 |
3.9%
|
|
| 2006 | 11 |
3.1%
|
|
| 2007 | 17 |
4.7%
|
|
| 2008 | 8 |
2.2%
|
|
| 2009 | 9 |
2.5%
|
|
| 2010 | 12 |
3.3%
|
|
| 2011 | 6 |
1.7%
|
|
| 2012 | 9 |
2.5%
|
|
| 2013 | 8 |
2.2%
|
|
| 2014 | 3 |
0.8%
|
|
| 2015 | 5 |
1.4%
|
|
| 2016 | 6 |
1.7%
|
|
| 2017 | 5 |
1.4%
|