| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 1 | 
                                    
                                    0.3%
                                 | 
| -7 | Does not apply | 19 | 
                                    
                                    5.2%
                                 | 
| 0 | No obstacle | 299 | 
                                    
                                    82.4%
                                 | 
| 1 | Minor obstacle | 19 | 
                                    
                                    5.2%
                                 | 
| 2 | Moderate obstacle | 11 | 
                                    
                                    3%
                                 | 
| 3 | Major obstacle | 10 | 
                                    
                                    2.8%
                                 | 
| 4 | Very severe obstacle | 4 | 
                                    
                                    1.1%
                                 |