| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 35 | 
                                                                 
                                    
                                    2.4%
                                 
                                                             | 
                                                        
                    
| -7 | Never regiestered (spontaneous) | 0 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    
| 1936 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1937 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1941 | 2 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1942 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1954 | 2 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1956 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1958 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1960 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1965 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1966 | 3 | 
                                                                 
                                    
                                    0.2%
                                 
                                                             | 
                                                        
                    |
| 1967 | 2 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1968 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1969 | 2 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1974 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1982 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1985 | 2 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1987 | 2 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1989 | 3 | 
                                                                 
                                    
                                    0.2%
                                 
                                                             | 
                                                        
                    |
| 1990 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1991 | 12 | 
                                                                 
                                    
                                    0.8%
                                 
                                                             | 
                                                        
                    |
| 1992 | 15 | 
                                                                 
                                    
                                    1%
                                 
                                                             | 
                                                        
                    |
| 1993 | 16 | 
                                                                 
                                    
                                    1.1%
                                 
                                                             | 
                                                        
                    |
| 1994 | 14 | 
                                                                 
                                    
                                    1%
                                 
                                                             | 
                                                        
                    |
| 1995 | 16 | 
                                                                 
                                    
                                    1.1%
                                 
                                                             | 
                                                        
                    |
| 1996 | 16 | 
                                                                 
                                    
                                    1.1%
                                 
                                                             | 
                                                        
                    |
| 1997 | 15 | 
                                                                 
                                    
                                    1%
                                 
                                                             | 
                                                        
                    |
| 1998 | 28 | 
                                                                 
                                    
                                    1.9%
                                 
                                                             | 
                                                        
                    |
| 1999 | 31 | 
                                                                 
                                    
                                    2.1%
                                 
                                                             | 
                                                        
                    |
| 2000 | 50 | 
                                                                 
                                    
                                    3.5%
                                 
                                                             | 
                                                        
                    |
| 2001 | 44 | 
                                                                 
                                    
                                    3%
                                 
                                                             | 
                                                        
                    |
| 2002 | 51 | 
                                                                 
                                    
                                    3.5%
                                 
                                                             | 
                                                        
                    |
| 2003 | 52 | 
                                                                 
                                    
                                    3.6%
                                 
                                                             | 
                                                        
                    |
| 2004 | 48 | 
                                                                 
                                    
                                    3.3%
                                 
                                                             | 
                                                        
                    |
| 2005 | 65 | 
                                                                 
                                    
                                    4.5%
                                 
                                                             | 
                                                        
                    |
| 2006 | 61 | 
                                                                 
                                    
                                    4.2%
                                 
                                                             | 
                                                        
                    |
| 2007 | 60 | 
                                                                 
                                    
                                    4.1%
                                 
                                                             | 
                                                        
                    |
| 2008 | 57 | 
                                                                 
                                    
                                    3.9%
                                 
                                                             | 
                                                        
                    |
| 2009 | 77 | 
                                                                 
                                    
                                    5.3%
                                 
                                                             | 
                                                        
                    |
| 2010 | 88 | 
                                                                 
                                    
                                    6.1%
                                 
                                                             | 
                                                        
                    |
| 2011 | 64 | 
                                                                 
                                    
                                    4.4%
                                 
                                                             | 
                                                        
                    |
| 2012 | 75 | 
                                                                 
                                    
                                    5.2%
                                 
                                                             | 
                                                        
                    |
| 2013 | 77 | 
                                                                 
                                    
                                    5.3%
                                 
                                                             | 
                                                        
                    |
| 2014 | 84 | 
                                                                 
                                    
                                    5.8%
                                 
                                                             | 
                                                        
                    |
| 2015 | 79 | 
                                                                 
                                    
                                    5.5%
                                 
                                                             | 
                                                        
                    |
| 2016 | 85 | 
                                                                 
                                    
                                    5.9%
                                 
                                                             | 
                                                        
                    |
| 2017 | 97 | 
                                                                 
                                    
                                    6.7%
                                 
                                                             | 
                                                        
                    |
| 2018 | 5 | 
                                                                 
                                    
                                    0.3%
                                 
                                                             |