| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 1 | 
                                    
                                    0.2%
                                 | 
| -7 | Does not apply | 4 | 
                                    
                                    1%
                                 | 
| 0 | No obstacle | 181 | 
                                    
                                    45%
                                 | 
| 1 | Minor obstacle | 66 | 
                                    
                                    16.4%
                                 | 
| 2 | Moderate obstacle | 73 | 
                                    
                                    18.2%
                                 | 
| 3 | Major obstacle | 47 | 
                                    
                                    11.7%
                                 | 
| 4 | Very severe obstacle | 30 | 
                                    
                                    7.5%
                                 |