| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 8 | 
                                    
                                    27.6%
                                 | 
| 2006 | 1 | 
                                    
                                    3.4%
                                 | |
| 2016 | 2 | 
                                    
                                    6.9%
                                 | |
| 2017 | 1 | 
                                    
                                    3.4%
                                 | |
| 2019 | 2 | 
                                    
                                    6.9%
                                 | |
| 2020 | 2 | 
                                    
                                    6.9%
                                 | |
| 2021 | 3 | 
                                    
                                    10.3%
                                 | |
| 2022 | 4 | 
                                    
                                    13.8%
                                 | |
| 2023 | 6 | 
                                    
                                    20.7%
                                 | |
| Sysmiss | 82 |