| Value | Category | Cases | |
|---|---|---|---|
| 1 | 1. Per month | 9 | 
                                                                 
                                    
                                    37.5%
                                 
                                                             | 
                                                        
                    
| 2 | 2. Per semester | 4 | 
                                                                 
                                    
                                    16.7%
                                 
                                                             | 
                                                        
                    
| 3 | 3. Per year | 5 | 
                                                                 
                                    
                                    20.8%
                                 
                                                             | 
                                                        
                    
| 5 | 5. Others | 6 | 
                                                                 
                                    
                                    25%
                                 
                                                             | 
                                                        
                    
| 6 | 6. None | 0 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    
| 9 | 9. Missing | 0 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    
| Sysmiss | 208 |