| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 4 |
1.5%
|
| 1957 | 1 |
0.4%
|
|
| 1960 | 1 |
0.4%
|
|
| 1964 | 1 |
0.4%
|
|
| 1969 | 1 |
0.4%
|
|
| 1970 | 1 |
0.4%
|
|
| 1972 | 2 |
0.7%
|
|
| 1974 | 1 |
0.4%
|
|
| 1975 | 1 |
0.4%
|
|
| 1976 | 1 |
0.4%
|
|
| 1979 | 1 |
0.4%
|
|
| 1980 | 2 |
0.7%
|
|
| 1982 | 1 |
0.4%
|
|
| 1983 | 2 |
0.7%
|
|
| 1985 | 3 |
1.1%
|
|
| 1986 | 1 |
0.4%
|
|
| 1987 | 4 |
1.5%
|
|
| 1988 | 4 |
1.5%
|
|
| 1989 | 9 |
3.3%
|
|
| 1990 | 9 |
3.3%
|
|
| 1991 | 6 |
2.2%
|
|
| 1992 | 6 |
2.2%
|
|
| 1993 | 6 |
2.2%
|
|
| 1994 | 4 |
1.5%
|
|
| 1995 | 2 |
0.7%
|
|
| 1996 | 4 |
1.5%
|
|
| 1997 | 2 |
0.7%
|
|
| 1999 | 7 |
2.6%
|
|
| 2000 | 27 |
10%
|
|
| 2001 | 9 |
3.3%
|
|
| 2002 | 10 |
3.7%
|
|
| 2003 | 13 |
4.8%
|
|
| 2004 | 9 |
3.3%
|
|
| 2005 | 11 |
4.1%
|
|
| 2006 | 9 |
3.3%
|
|
| 2007 | 11 |
4.1%
|
|
| 2008 | 10 |
3.7%
|
|
| 2009 | 9 |
3.3%
|
|
| 2010 | 13 |
4.8%
|
|
| 2011 | 7 |
2.6%
|
|
| 2012 | 7 |
2.6%
|
|
| 2013 | 5 |
1.8%
|
|
| 2014 | 9 |
3.3%
|
|
| 2015 | 4 |
1.5%
|
|
| 2016 | 10 |
3.7%
|
|
| 2017 | 11 |
4.1%
|