| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 6 | 
                                                                 
                                    
                                    0.8%
                                 
                                                             | 
                                                        
                    
| -7 | Never regiestered (spontaneous) | 0 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    
| 1926 | 2 | 
                                                                 
                                    
                                    0.3%
                                 
                                                             | 
                                                        
                    |
| 1936 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1951 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1954 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1955 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1959 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1960 | 2 | 
                                                                 
                                    
                                    0.3%
                                 
                                                             | 
                                                        
                    |
| 1962 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1964 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1965 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1966 | 2 | 
                                                                 
                                    
                                    0.3%
                                 
                                                             | 
                                                        
                    |
| 1967 | 3 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1968 | 2 | 
                                                                 
                                    
                                    0.3%
                                 
                                                             | 
                                                        
                    |
| 1971 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1974 | 3 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1975 | 2 | 
                                                                 
                                    
                                    0.3%
                                 
                                                             | 
                                                        
                    |
| 1976 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1977 | 2 | 
                                                                 
                                    
                                    0.3%
                                 
                                                             | 
                                                        
                    |
| 1979 | 1 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1987 | 2 | 
                                                                 
                                    
                                    0.3%
                                 
                                                             | 
                                                        
                    |
| 1988 | 2 | 
                                                                 
                                    
                                    0.3%
                                 
                                                             | 
                                                        
                    |
| 1989 | 8 | 
                                                                 
                                    
                                    1%
                                 
                                                             | 
                                                        
                    |
| 1990 | 13 | 
                                                                 
                                    
                                    1.7%
                                 
                                                             | 
                                                        
                    |
| 1991 | 25 | 
                                                                 
                                    
                                    3.2%
                                 
                                                             | 
                                                        
                    |
| 1992 | 34 | 
                                                                 
                                    
                                    4.4%
                                 
                                                             | 
                                                        
                    |
| 1993 | 19 | 
                                                                 
                                    
                                    2.5%
                                 
                                                             | 
                                                        
                    |
| 1994 | 29 | 
                                                                 
                                    
                                    3.8%
                                 
                                                             | 
                                                        
                    |
| 1995 | 20 | 
                                                                 
                                    
                                    2.6%
                                 
                                                             | 
                                                        
                    |
| 1996 | 30 | 
                                                                 
                                    
                                    3.9%
                                 
                                                             | 
                                                        
                    |
| 1997 | 27 | 
                                                                 
                                    
                                    3.5%
                                 
                                                             | 
                                                        
                    |
| 1998 | 25 | 
                                                                 
                                    
                                    3.2%
                                 
                                                             | 
                                                        
                    |
| 1999 | 25 | 
                                                                 
                                    
                                    3.2%
                                 
                                                             | 
                                                        
                    |
| 2000 | 20 | 
                                                                 
                                    
                                    2.6%
                                 
                                                             | 
                                                        
                    |
| 2001 | 21 | 
                                                                 
                                    
                                    2.7%
                                 
                                                             | 
                                                        
                    |
| 2002 | 30 | 
                                                                 
                                    
                                    3.9%
                                 
                                                             | 
                                                        
                    |
| 2003 | 27 | 
                                                                 
                                    
                                    3.5%
                                 
                                                             | 
                                                        
                    |
| 2004 | 31 | 
                                                                 
                                    
                                    4%
                                 
                                                             | 
                                                        
                    |
| 2005 | 24 | 
                                                                 
                                    
                                    3.1%
                                 
                                                             | 
                                                        
                    |
| 2006 | 20 | 
                                                                 
                                    
                                    2.6%
                                 
                                                             | 
                                                        
                    |
| 2007 | 25 | 
                                                                 
                                    
                                    3.2%
                                 
                                                             | 
                                                        
                    |
| 2008 | 92 | 
                                                                 
                                    
                                    11.9%
                                 
                                                             | 
                                                        
                    |
| 2009 | 41 | 
                                                                 
                                    
                                    5.3%
                                 
                                                             | 
                                                        
                    |
| 2010 | 41 | 
                                                                 
                                    
                                    5.3%
                                 
                                                             | 
                                                        
                    |
| 2011 | 17 | 
                                                                 
                                    
                                    2.2%
                                 
                                                             | 
                                                        
                    |
| 2012 | 16 | 
                                                                 
                                    
                                    2.1%
                                 
                                                             | 
                                                        
                    |
| 2013 | 32 | 
                                                                 
                                    
                                    4.1%
                                 
                                                             | 
                                                        
                    |
| 2014 | 10 | 
                                                                 
                                    
                                    1.3%
                                 
                                                             | 
                                                        
                    |
| 2015 | 13 | 
                                                                 
                                    
                                    1.7%
                                 
                                                             | 
                                                        
                    |
| 2016 | 14 | 
                                                                 
                                    
                                    1.8%
                                 
                                                             | 
                                                        
                    |
| 2017 | 4 | 
                                                                 
                                    
                                    0.5%
                                 
                                                             |