| Value | Category | Cases | |
|---|---|---|---|
| 10 | Once in 4 years | 10 | 
                                    
                                    8.9%
                                 | 
| 11 | once in 5 years | 46 | 
                                    
                                    41.1%
                                 | 
| 12 | Does not specify the time | 56 | 
                                    
                                    50%
                                 | 
| Sysmiss | 1855 |