| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 15 | 
                                    
                                    55.6%
                                 | 
| 1999 | 1 | 
                                    
                                    3.7%
                                 | |
| 2000 | 2 | 
                                    
                                    7.4%
                                 | |
| 2005 | 1 | 
                                    
                                    3.7%
                                 | |
| 2007 | 2 | 
                                    
                                    7.4%
                                 | |
| 2009 | 1 | 
                                    
                                    3.7%
                                 | |
| 2012 | 1 | 
                                    
                                    3.7%
                                 | |
| 2019 | 1 | 
                                    
                                    3.7%
                                 | |
| 2021 | 1 | 
                                    
                                    3.7%
                                 | |
| 2023 | 2 | 
                                    
                                    7.4%
                                 | |
| Sysmiss | 84 |