| Value | Category | Cases | |
|---|---|---|---|
| 1 | 1. Per month | 10 | 
                                                                 
                                    
                                    32.3%
                                 
                                                             | 
                                                        
                    
| 2 | 2. Per semester | 5 | 
                                                                 
                                    
                                    16.1%
                                 
                                                             | 
                                                        
                    
| 3 | 3. Per year | 15 | 
                                                                 
                                    
                                    48.4%
                                 
                                                             | 
                                                        
                    
| 5 | 5. Others | 1 | 
                                                                 
                                    
                                    3.2%
                                 
                                                             | 
                                                        
                    
| 6 | 6. None | 0 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    
| 9 | 9. Missing | 0 | 
                                                                 
                                    
                                    0%
                                 
                                                             | 
                                                        
                    
| Sysmiss | 308 |