| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 0 | 
                                    
                                    0%
                                 | 
| -7 | Does not apply | 0 | 
                                    
                                    0%
                                 | 
| 0 | No obstacle | 297 | 
                                    
                                    95.5%
                                 | 
| 1 | Minor obstacle | 11 | 
                                    
                                    3.5%
                                 | 
| 2 | Moderate obstacle | 1 | 
                                    
                                    0.3%
                                 | 
| 3 | Major obstacle | 2 | 
                                    
                                    0.6%
                                 | 
| 4 | Very severe obstacle | 0 | 
                                    
                                    0%
                                 |