| Value | Category | Cases | |
|---|---|---|---|
| -9 | Don't know (spontaneous) | 1 | 
                                    
                                    0.2%
                                 | 
| -7 | Does not apply | 2 | 
                                    
                                    0.3%
                                 | 
| 0 | No obstacle | 421 | 
                                    
                                    68.8%
                                 | 
| 1 | Minor obstacle | 115 | 
                                    
                                    18.8%
                                 | 
| 2 | Moderate obstacle | 45 | 
                                    
                                    7.4%
                                 | 
| 3 | Major obstacle | 19 | 
                                    
                                    3.1%
                                 | 
| 4 | Very severe obstacle | 9 | 
                                    
                                    1.5%
                                 |