| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 1 | 
                                    
                                    0.2%
                                 | 
| -7 | Never regiestered (spontaneous) | 0 | 
                                    
                                    0%
                                 | 
| 1873 | 1 | 
                                    
                                    0.2%
                                 | |
| 1908 | 1 | 
                                    
                                    0.2%
                                 | |
| 1929 | 1 | 
                                    
                                    0.2%
                                 | |
| 1945 | 2 | 
                                    
                                    0.5%
                                 | |
| 1946 | 1 | 
                                    
                                    0.2%
                                 | |
| 1947 | 3 | 
                                    
                                    0.7%
                                 | |
| 1948 | 2 | 
                                    
                                    0.5%
                                 | |
| 1950 | 1 | 
                                    
                                    0.2%
                                 | |
| 1952 | 1 | 
                                    
                                    0.2%
                                 | |
| 1954 | 2 | 
                                    
                                    0.5%
                                 | |
| 1955 | 3 | 
                                    
                                    0.7%
                                 | |
| 1956 | 1 | 
                                    
                                    0.2%
                                 | |
| 1959 | 1 | 
                                    
                                    0.2%
                                 | |
| 1960 | 2 | 
                                    
                                    0.5%
                                 | |
| 1962 | 1 | 
                                    
                                    0.2%
                                 | |
| 1963 | 1 | 
                                    
                                    0.2%
                                 | |
| 1964 | 3 | 
                                    
                                    0.7%
                                 | |
| 1965 | 1 | 
                                    
                                    0.2%
                                 | |
| 1969 | 1 | 
                                    
                                    0.2%
                                 | |
| 1972 | 1 | 
                                    
                                    0.2%
                                 | |
| 1974 | 4 | 
                                    
                                    1%
                                 | |
| 1975 | 1 | 
                                    
                                    0.2%
                                 | |
| 1976 | 1 | 
                                    
                                    0.2%
                                 | |
| 1977 | 3 | 
                                    
                                    0.7%
                                 | |
| 1978 | 2 | 
                                    
                                    0.5%
                                 | |
| 1980 | 1 | 
                                    
                                    0.2%
                                 | |
| 1982 | 2 | 
                                    
                                    0.5%
                                 | |
| 1983 | 1 | 
                                    
                                    0.2%
                                 | |
| 1984 | 4 | 
                                    
                                    1%
                                 | |
| 1985 | 3 | 
                                    
                                    0.7%
                                 | |
| 1986 | 1 | 
                                    
                                    0.2%
                                 | |
| 1987 | 1 | 
                                    
                                    0.2%
                                 | |
| 1988 | 2 | 
                                    
                                    0.5%
                                 | |
| 1989 | 18 | 
                                    
                                    4.5%
                                 | |
| 1990 | 37 | 
                                    
                                    9.2%
                                 | |
| 1991 | 34 | 
                                    
                                    8.5%
                                 | |
| 1992 | 20 | 
                                    
                                    5%
                                 | |
| 1993 | 16 | 
                                    
                                    4%
                                 | |
| 1994 | 12 | 
                                    
                                    3%
                                 | |
| 1995 | 9 | 
                                    
                                    2.2%
                                 | |
| 1996 | 13 | 
                                    
                                    3.2%
                                 | |
| 1997 | 9 | 
                                    
                                    2.2%
                                 | |
| 1998 | 6 | 
                                    
                                    1.5%
                                 | |
| 1999 | 9 | 
                                    
                                    2.2%
                                 | |
| 2000 | 3 | 
                                    
                                    0.7%
                                 | |
| 2001 | 13 | 
                                    
                                    3.2%
                                 | |
| 2002 | 5 | 
                                    
                                    1.2%
                                 | |
| 2003 | 4 | 
                                    
                                    1%
                                 | |
| 2004 | 5 | 
                                    
                                    1.2%
                                 | |
| 2005 | 5 | 
                                    
                                    1.2%
                                 | |
| 2006 | 9 | 
                                    
                                    2.2%
                                 | |
| 2007 | 12 | 
                                    
                                    3%
                                 | |
| 2008 | 6 | 
                                    
                                    1.5%
                                 | |
| 2009 | 8 | 
                                    
                                    2%
                                 | |
| 2010 | 16 | 
                                    
                                    4%
                                 | |
| 2011 | 11 | 
                                    
                                    2.7%
                                 | |
| 2012 | 8 | 
                                    
                                    2%
                                 | |
| 2013 | 10 | 
                                    
                                    2.5%
                                 | |
| 2014 | 12 | 
                                    
                                    3%
                                 | |
| 2015 | 14 | 
                                    
                                    3.5%
                                 | |
| 2016 | 4 | 
                                    
                                    1%
                                 | |
| 2017 | 4 | 
                                    
                                    1%
                                 | |
| 2018 | 4 | 
                                    
                                    1%
                                 | |
| 2019 | 5 | 
                                    
                                    1.2%
                                 | |
| 2021 | 2 | 
                                    
                                    0.5%
                                 | |
| 2022 | 2 | 
                                    
                                    0.5%
                                 |