| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 4 | 
                                    
                                    1.1%
                                 | 
| -7 | Does not apply | 12 | 
                                    
                                    3.3%
                                 | 
| 0 | No obstacle | 255 | 
                                    
                                    70.2%
                                 | 
| 1 | Minor obstacle | 37 | 
                                    
                                    10.2%
                                 | 
| 2 | Moderate obstacle | 35 | 
                                    
                                    9.6%
                                 | 
| 3 | Major obstacle | 17 | 
                                    
                                    4.7%
                                 | 
| 4 | Very severe obstacle | 3 | 
                                    
                                    0.8%
                                 |