| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 3 | 
                                    
                                    0.8%
                                 | 
| -7 | Never regiestered (spontaneous) | 0 | 
                                    
                                    0%
                                 | 
| 1975 | 1 | 
                                    
                                    0.3%
                                 | |
| 1980 | 1 | 
                                    
                                    0.3%
                                 | |
| 1986 | 1 | 
                                    
                                    0.3%
                                 | |
| 1987 | 1 | 
                                    
                                    0.3%
                                 | |
| 1989 | 3 | 
                                    
                                    0.8%
                                 | |
| 1990 | 7 | 
                                    
                                    1.9%
                                 | |
| 1991 | 6 | 
                                    
                                    1.7%
                                 | |
| 1992 | 4 | 
                                    
                                    1.1%
                                 | |
| 1993 | 1 | 
                                    
                                    0.3%
                                 | |
| 1994 | 5 | 
                                    
                                    1.4%
                                 | |
| 1995 | 4 | 
                                    
                                    1.1%
                                 | |
| 1996 | 6 | 
                                    
                                    1.7%
                                 | |
| 1997 | 5 | 
                                    
                                    1.4%
                                 | |
| 1998 | 4 | 
                                    
                                    1.1%
                                 | |
| 1999 | 3 | 
                                    
                                    0.8%
                                 | |
| 2000 | 21 | 
                                    
                                    5.8%
                                 | |
| 2001 | 2 | 
                                    
                                    0.6%
                                 | |
| 2002 | 8 | 
                                    
                                    2.2%
                                 | |
| 2003 | 8 | 
                                    
                                    2.2%
                                 | |
| 2004 | 10 | 
                                    
                                    2.8%
                                 | |
| 2005 | 12 | 
                                    
                                    3.3%
                                 | |
| 2006 | 10 | 
                                    
                                    2.8%
                                 | |
| 2007 | 8 | 
                                    
                                    2.2%
                                 | |
| 2008 | 15 | 
                                    
                                    4.1%
                                 | |
| 2009 | 17 | 
                                    
                                    4.7%
                                 | |
| 2010 | 15 | 
                                    
                                    4.1%
                                 | |
| 2011 | 21 | 
                                    
                                    5.8%
                                 | |
| 2012 | 30 | 
                                    
                                    8.3%
                                 | |
| 2013 | 22 | 
                                    
                                    6.1%
                                 | |
| 2014 | 18 | 
                                    
                                    5%
                                 | |
| 2015 | 13 | 
                                    
                                    3.6%
                                 | |
| 2016 | 15 | 
                                    
                                    4.1%
                                 | |
| 2017 | 17 | 
                                    
                                    4.7%
                                 | |
| 2018 | 17 | 
                                    
                                    4.7%
                                 | |
| 2019 | 11 | 
                                    
                                    3%
                                 | |
| 2020 | 7 | 
                                    
                                    1.9%
                                 | |
| 2021 | 3 | 
                                    
                                    0.8%
                                 | |
| 2022 | 2 | 
                                    
                                    0.6%
                                 | |
| 2023 | 6 | 
                                    
                                    1.7%
                                 |