| Value | Category | Cases | |
|---|---|---|---|
| 1 | Not effective at all | 2 | 
                                    
                                    1.8%
                                 | 
| 2 | 2 | 
                                    
                                    1.8%
                                 | |
| 3 | 4 | 
                                    
                                    3.6%
                                 | |
| 4 | 6 | 
                                    
                                    5.4%
                                 | |
| 5 | 13 | 
                                    
                                    11.6%
                                 | |
| 6 | 12 | 
                                    
                                    10.7%
                                 | |
| 7 | 20 | 
                                    
                                    17.9%
                                 | |
| 8 | 31 | 
                                    
                                    27.7%
                                 | |
| 9 | 14 | 
                                    
                                    12.5%
                                 | |
| 10 | Very effective | 6 | 
                                    
                                    5.4%
                                 | 
| 11 | Don't know | 2 | 
                                    
                                    1.8%
                                 |