| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 1 | 
                                    
                                    0.1%
                                 | 
| -7 | Does not apply | 30 | 
                                    
                                    2.9%
                                 | 
| 0 | No obstacle | 810 | 
                                    
                                    79.1%
                                 | 
| 1 | Minor obstacle | 126 | 
                                    
                                    12.3%
                                 | 
| 2 | Moderate obstacle | 33 | 
                                    
                                    3.2%
                                 | 
| 3 | Major obstacle | 16 | 
                                    
                                    1.6%
                                 | 
| 4 | Very severe obstacle | 8 | 
                                    
                                    0.8%
                                 |