| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 29 | 
                                    
                                    3%
                                 | 
| -8 | 1 | 
                                    
                                    0.1%
                                 | |
| -7 | Does not apply | 20 | 
                                    
                                    2.1%
                                 | 
| 0 | No obstacle | 587 | 
                                    
                                    61.5%
                                 | 
| 1 | Minor obstacle | 129 | 
                                    
                                    13.5%
                                 | 
| 2 | Moderate obstacle | 87 | 
                                    
                                    9.1%
                                 | 
| 3 | Major obstacle | 71 | 
                                    
                                    7.4%
                                 | 
| 4 | Very severe obstacle | 31 | 
                                    
                                    3.2%
                                 |