| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 293 | 
                                                                 
                                    
                                    2.7%
                                 
                                                             | 
                                                        
                    
| 1958 | 1 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    |
| 1960 | 1 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    |
| 1965 | 4 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    |
| 1966 | 2 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    |
| 1969 | 1 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    |
| 1970 | 16 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1971 | 1 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    |
| 1972 | 5 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    |
| 1974 | 2 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    |
| 1975 | 11 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1976 | 3 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    |
| 1977 | 2 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    |
| 1978 | 5 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    |
| 1979 | 1 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    |
| 1980 | 41 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1981 | 3 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    |
| 1982 | 9 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1983 | 4 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    |
| 1984 | 6 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1985 | 50 | 
                                                                 
                                    
                                    0.5%
                                 
                                                             | 
                                                        
                    |
| 1986 | 12 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1987 | 18 | 
                                                                 
                                    
                                    0.2%
                                 
                                                             | 
                                                        
                    |
| 1988 | 15 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1989 | 24 | 
                                                                 
                                    
                                    0.2%
                                 
                                                             | 
                                                        
                    |
| 1990 | 68 | 
                                                                 
                                    
                                    0.6%
                                 
                                                             | 
                                                        
                    |
| 1991 | 22 | 
                                                                 
                                    
                                    0.2%
                                 
                                                             | 
                                                        
                    |
| 1992 | 24 | 
                                                                 
                                    
                                    0.2%
                                 
                                                             | 
                                                        
                    |
| 1993 | 16 | 
                                                                 
                                    
                                    0.1%
                                 
                                                             | 
                                                        
                    |
| 1994 | 19 | 
                                                                 
                                    
                                    0.2%
                                 
                                                             | 
                                                        
                    |
| 1995 | 94 | 
                                                                 
                                    
                                    0.9%
                                 
                                                             | 
                                                        
                    |
| 1996 | 46 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1997 | 44 | 
                                                                 
                                    
                                    0.4%
                                 
                                                             | 
                                                        
                    |
| 1998 | 122 | 
                                                                 
                                    
                                    1.1%
                                 
                                                             | 
                                                        
                    |
| 1999 | 128 | 
                                                                 
                                    
                                    1.2%
                                 
                                                             | 
                                                        
                    |
| 2000 | 387 | 
                                                                 
                                    
                                    3.6%
                                 
                                                             | 
                                                        
                    |
| 2001 | 249 | 
                                                                 
                                    
                                    2.3%
                                 
                                                             | 
                                                        
                    |
| 2002 | 113 | 
                                                                 
                                    
                                    1.1%
                                 
                                                             | 
                                                        
                    |
| 2003 | 75 | 
                                                                 
                                    
                                    0.7%
                                 
                                                             | 
                                                        
                    |
| 2004 | 104 | 
                                                                 
                                    
                                    1%
                                 
                                                             | 
                                                        
                    |
| 2005 | 328 | 
                                                                 
                                    
                                    3.1%
                                 
                                                             | 
                                                        
                    |
| 2006 | 178 | 
                                                                 
                                    
                                    1.7%
                                 
                                                             | 
                                                        
                    |
| 2007 | 103 | 
                                                                 
                                    
                                    1%
                                 
                                                             | 
                                                        
                    |
| 2008 | 362 | 
                                                                 
                                    
                                    3.4%
                                 
                                                             | 
                                                        
                    |
| 2009 | 446 | 
                                                                 
                                    
                                    4.2%
                                 
                                                             | 
                                                        
                    |
| 2010 | 763 | 
                                                                 
                                    
                                    7.1%
                                 
                                                             | 
                                                        
                    |
| 2011 | 449 | 
                                                                 
                                    
                                    4.2%
                                 
                                                             | 
                                                        
                    |
| 2012 | 538 | 
                                                                 
                                    
                                    5%
                                 
                                                             | 
                                                        
                    |
| 2013 | 341 | 
                                                                 
                                    
                                    3.2%
                                 
                                                             | 
                                                        
                    |
| 2014 | 704 | 
                                                                 
                                    
                                    6.6%
                                 
                                                             | 
                                                        
                    |
| 2015 | 1112 | 
                                                                 
                                    
                                    10.4%
                                 
                                                             | 
                                                        
                    |
| 2016 | 907 | 
                                                                 
                                    
                                    8.5%
                                 
                                                             | 
                                                        
                    |
| 2017 | 707 | 
                                                                 
                                    
                                    6.6%
                                 
                                                             | 
                                                        
                    |
| 2018 | 765 | 
                                                                 
                                    
                                    7.2%
                                 
                                                             | 
                                                        
                    |
| 2019 | 496 | 
                                                                 
                                    
                                    4.6%
                                 
                                                             | 
                                                        
                    |
| 2020 | 245 | 
                                                                 
                                    
                                    2.3%
                                 
                                                             | 
                                                        
                    |
| 2021 | 150 | 
                                                                 
                                    
                                    1.4%
                                 
                                                             | 
                                                        
                    |
| 2022 | 37 | 
                                                                 
                                    
                                    0.3%
                                 
                                                             |