| Value | Category | Cases | |
|---|---|---|---|
| 0 | 57 | 
                                    
                                    4.9%
                                 | |
| 1 | Before 1990 | 430 | 
                                    
                                    36.7%
                                 | 
| 2 | From 1990-95 | 193 | 
                                    
                                    16.5%
                                 | 
| 3 | since 1995 | 370 | 
                                    
                                    31.6%
                                 | 
| 4 | 2001-2002 | 82 | 
                                    
                                    7%
                                 | 
| 9 | Don't know | 39 | 
                                    
                                    3.3%
                                 | 
| Sysmiss | 1762 |