| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 1 | 
                                    
                                    0.2%
                                 | 
| -7 | Does not apply | 21 | 
                                    
                                    5.2%
                                 | 
| 0 | No obstacle | 252 | 
                                    
                                    62.7%
                                 | 
| 1 | Minor obstacle | 64 | 
                                    
                                    15.9%
                                 | 
| 2 | Moderate obstacle | 42 | 
                                    
                                    10.4%
                                 | 
| 3 | Major obstacle | 18 | 
                                    
                                    4.5%
                                 | 
| 4 | Very severe obstacle | 4 | 
                                    
                                    1%
                                 |