| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 21 | 
                                                                 
                                    
                                    9%
                                 
                                                             | 
                                                        
                    
| -7 | Never regiestered (spontaneous) | 0 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    
| 1903 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1920 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1933 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1935 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1938 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1939 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1942 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1945 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1948 | 3 | 
                                                                 
                                    
                                    1.3%
                                 
                                                             | 
                                                        
                    |
| 1951 | 2 | 
                                                                 
                                    
                                    0.9%
                                 
                                                             | 
                                                        
                    |
| 1954 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1956 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1957 | 2 | 
                                                                 
                                    
                                    0.9%
                                 
                                                             | 
                                                        
                    |
| 1958 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1959 | 2 | 
                                                                 
                                    
                                    0.9%
                                 
                                                             | 
                                                        
                    |
| 1966 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1967 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1968 | 2 | 
                                                                 
                                    
                                    0.9%
                                 
                                                             | 
                                                        
                    |
| 1969 | 3 | 
                                                                 
                                    
                                    1.3%
                                 
                                                             | 
                                                        
                    |
| 1970 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1971 | 3 | 
                                                                 
                                    
                                    1.3%
                                 
                                                             | 
                                                        
                    |
| 1973 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1975 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1976 | 3 | 
                                                                 
                                    
                                    1.3%
                                 
                                                             | 
                                                        
                    |
| 1977 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1978 | 2 | 
                                                                 
                                    
                                    0.9%
                                 
                                                             | 
                                                        
                    |
| 1980 | 6 | 
                                                                 
                                    
                                    2.6%
                                 
                                                             | 
                                                        
                    |
| 1981 | 2 | 
                                                                 
                                    
                                    0.9%
                                 
                                                             | 
                                                        
                    |
| 1982 | 3 | 
                                                                 
                                    
                                    1.3%
                                 
                                                             | 
                                                        
                    |
| 1983 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1984 | 2 | 
                                                                 
                                    
                                    0.9%
                                 
                                                             | 
                                                        
                    |
| 1985 | 2 | 
                                                                 
                                    
                                    0.9%
                                 
                                                             | 
                                                        
                    |
| 1987 | 2 | 
                                                                 
                                    
                                    0.9%
                                 
                                                             | 
                                                        
                    |
| 1988 | 2 | 
                                                                 
                                    
                                    0.9%
                                 
                                                             | 
                                                        
                    |
| 1989 | 4 | 
                                                                 
                                    
                                    1.7%
                                 
                                                             | 
                                                        
                    |
| 1990 | 8 | 
                                                                 
                                    
                                    3.4%
                                 
                                                             | 
                                                        
                    |
| 1991 | 2 | 
                                                                 
                                    
                                    0.9%
                                 
                                                             | 
                                                        
                    |
| 1992 | 3 | 
                                                                 
                                    
                                    1.3%
                                 
                                                             | 
                                                        
                    |
| 1993 | 6 | 
                                                                 
                                    
                                    2.6%
                                 
                                                             | 
                                                        
                    |
| 1994 | 3 | 
                                                                 
                                    
                                    1.3%
                                 
                                                             | 
                                                        
                    |
| 1995 | 4 | 
                                                                 
                                    
                                    1.7%
                                 
                                                             | 
                                                        
                    |
| 1996 | 6 | 
                                                                 
                                    
                                    2.6%
                                 
                                                             | 
                                                        
                    |
| 1997 | 10 | 
                                                                 
                                    
                                    4.3%
                                 
                                                             | 
                                                        
                    |
| 1998 | 6 | 
                                                                 
                                    
                                    2.6%
                                 
                                                             | 
                                                        
                    |
| 1999 | 6 | 
                                                                 
                                    
                                    2.6%
                                 
                                                             | 
                                                        
                    |
| 2000 | 8 | 
                                                                 
                                    
                                    3.4%
                                 
                                                             | 
                                                        
                    |
| 2001 | 4 | 
                                                                 
                                    
                                    1.7%
                                 
                                                             | 
                                                        
                    |
| 2002 | 6 | 
                                                                 
                                    
                                    2.6%
                                 
                                                             | 
                                                        
                    |
| 2003 | 7 | 
                                                                 
                                    
                                    3%
                                 
                                                             | 
                                                        
                    |
| 2004 | 5 | 
                                                                 
                                    
                                    2.1%
                                 
                                                             | 
                                                        
                    |
| 2005 | 10 | 
                                                                 
                                    
                                    4.3%
                                 
                                                             | 
                                                        
                    |
| 2006 | 8 | 
                                                                 
                                    
                                    3.4%
                                 
                                                             | 
                                                        
                    |
| 2007 | 4 | 
                                                                 
                                    
                                    1.7%
                                 
                                                             | 
                                                        
                    |
| 2008 | 7 | 
                                                                 
                                    
                                    3%
                                 
                                                             | 
                                                        
                    |
| 2009 | 6 | 
                                                                 
                                    
                                    2.6%
                                 
                                                             | 
                                                        
                    |
| 2010 | 8 | 
                                                                 
                                    
                                    3.4%
                                 
                                                             | 
                                                        
                    |
| 2011 | 3 | 
                                                                 
                                    
                                    1.3%
                                 
                                                             | 
                                                        
                    |
| 2012 | 8 | 
                                                                 
                                    
                                    3.4%
                                 
                                                             | 
                                                        
                    |
| 2013 | 2 | 
                                                                 
                                    
                                    0.9%
                                 
                                                             | 
                                                        
                    |
| 2014 | 4 | 
                                                                 
                                    
                                    1.7%
                                 
                                                             | 
                                                        
                    |
| 2015 | 4 | 
                                                                 
                                    
                                    1.7%
                                 
                                                             | 
                                                        
                    |
| 2016 | 1 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             |