| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 3 | 
                                    
                                    3.4%
                                 | 
| 1975 | 1 | 
                                    
                                    1.1%
                                 | |
| 1987 | 1 | 
                                    
                                    1.1%
                                 | |
| 1991 | 2 | 
                                    
                                    2.2%
                                 | |
| 1992 | 1 | 
                                    
                                    1.1%
                                 | |
| 1993 | 1 | 
                                    
                                    1.1%
                                 | |
| 1994 | 1 | 
                                    
                                    1.1%
                                 | |
| 1995 | 1 | 
                                    
                                    1.1%
                                 | |
| 2000 | 5 | 
                                    
                                    5.6%
                                 | |
| 2001 | 1 | 
                                    
                                    1.1%
                                 | |
| 2003 | 2 | 
                                    
                                    2.2%
                                 | |
| 2004 | 3 | 
                                    
                                    3.4%
                                 | |
| 2005 | 2 | 
                                    
                                    2.2%
                                 | |
| 2006 | 3 | 
                                    
                                    3.4%
                                 | |
| 2007 | 2 | 
                                    
                                    2.2%
                                 | |
| 2008 | 2 | 
                                    
                                    2.2%
                                 | |
| 2009 | 2 | 
                                    
                                    2.2%
                                 | |
| 2010 | 5 | 
                                    
                                    5.6%
                                 | |
| 2011 | 1 | 
                                    
                                    1.1%
                                 | |
| 2012 | 6 | 
                                    
                                    6.7%
                                 | |
| 2013 | 6 | 
                                    
                                    6.7%
                                 | |
| 2014 | 3 | 
                                    
                                    3.4%
                                 | |
| 2015 | 2 | 
                                    
                                    2.2%
                                 | |
| 2016 | 4 | 
                                    
                                    4.5%
                                 | |
| 2017 | 6 | 
                                    
                                    6.7%
                                 | |
| 2018 | 3 | 
                                    
                                    3.4%
                                 | |
| 2019 | 4 | 
                                    
                                    4.5%
                                 | |
| 2020 | 4 | 
                                    
                                    4.5%
                                 | |
| 2021 | 1 | 
                                    
                                    1.1%
                                 | |
| 2022 | 6 | 
                                    
                                    6.7%
                                 | |
| 2023 | 5 | 
                                    
                                    5.6%
                                 | |
| Sysmiss | 274 |