| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 6 | 
                                    
                                    1.3%
                                 | 
| 2001 | 1 | 
                                    
                                    0.2%
                                 | |
| 2004 | 2 | 
                                    
                                    0.4%
                                 | |
| 2005 | 2 | 
                                    
                                    0.4%
                                 | |
| 2006 | 3 | 
                                    
                                    0.7%
                                 | |
| 2007 | 4 | 
                                    
                                    0.9%
                                 | |
| 2008 | 8 | 
                                    
                                    1.8%
                                 | |
| 2009 | 3 | 
                                    
                                    0.7%
                                 | |
| 2010 | 10 | 
                                    
                                    2.2%
                                 | |
| 2011 | 28 | 
                                    
                                    6.1%
                                 | |
| 2012 | 74 | 
                                    
                                    16.2%
                                 | |
| 2013 | 60 | 
                                    
                                    13.2%
                                 | |
| 2014 | 7 | 
                                    
                                    1.5%
                                 | |
| 2015 | 19 | 
                                    
                                    4.2%
                                 | |
| 2016 | 26 | 
                                    
                                    5.7%
                                 | |
| 2017 | 38 | 
                                    
                                    8.3%
                                 | |
| 2018 | 103 | 
                                    
                                    22.6%
                                 | |
| 2019 | 62 | 
                                    
                                    13.6%
                                 | |
| Sysmiss | 499 |