| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 3 | 
                                    
                                    0.2%
                                 | 
| -7 | Does not apply | 30 | 
                                    
                                    2.1%
                                 | 
| 0 | No obstacle | 973 | 
                                    
                                    68.7%
                                 | 
| 1 | Minor obstacle | 152 | 
                                    
                                    10.7%
                                 | 
| 2 | Moderate obstacle | 83 | 
                                    
                                    5.9%
                                 | 
| 3 | Major obstacle | 94 | 
                                    
                                    6.6%
                                 | 
| 4 | Very severe obstacle | 81 | 
                                    
                                    5.7%
                                 |