| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 2 | 
                                    
                                    0.6%
                                 | 
| -7 | Does not apply | 38 | 
                                    
                                    12.2%
                                 | 
| 0 | No obstacle | 252 | 
                                    
                                    81%
                                 | 
| 1 | Minor obstacle | 3 | 
                                    
                                    1%
                                 | 
| 2 | Moderate obstacle | 5 | 
                                    
                                    1.6%
                                 | 
| 3 | Major obstacle | 6 | 
                                    
                                    1.9%
                                 | 
| 4 | Very severe obstacle | 5 | 
                                    
                                    1.6%
                                 |