| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 1 | 
                                    
                                    0.1%
                                 | 
| -7 | Does not apply | 2 | 
                                    
                                    0.2%
                                 | 
| 0 | No obstacle | 586 | 
                                    
                                    57.2%
                                 | 
| 1 | Minor obstacle | 255 | 
                                    
                                    24.9%
                                 | 
| 2 | Moderate obstacle | 107 | 
                                    
                                    10.4%
                                 | 
| 3 | Major obstacle | 66 | 
                                    
                                    6.4%
                                 | 
| 4 | Very severe obstacle | 7 | 
                                    
                                    0.7%
                                 |