| Value | Category | Cases | |
|---|---|---|---|
| -999 | -999 | 4 | 
                                                                 
                                    
                                    3.3%
                                 
                                                             | 
                                                        
                    
| -888 | -888 | 26 | 
                                                                 
                                    
                                    21.7%
                                 
                                                             | 
                                                        
                    
| 1 | More than one month | 11 | 
                                                                 
                                    
                                    9.2%
                                 
                                                             | 
                                                        
                    
| 2 | Once every month | 7 | 
                                                                 
                                    
                                    5.8%
                                 
                                                             | 
                                                        
                    
| 3 | Once every two months | 6 | 
                                                                 
                                    
                                    5%
                                 
                                                             | 
                                                        
                    
| 4 | Once every three months | 37 | 
                                                                 
                                    
                                    30.8%
                                 
                                                             | 
                                                        
                    
| 5 | Less than once every three months | 29 | 
                                                                 
                                    
                                    24.2%
                                 
                                                             | 
                                                        
                    
| Sysmiss | 792 |