| Value | Category | 
                                    
                    
                        | 1 | still in training | 
                                    
                    
                        | 2 | 1998 | 
                                    
                    
                        | 3 | 1997 | 
                                    
                    
                        | 4 | 1996 | 
                                    
                    
                        | 5 | 1995 | 
                                    
                    
                        | 6 | 1994 | 
                                    
                    
                        | 7 | 1993 or before | 
                                    
                    
                        | 9 | no answer | 
                            
            Warning: these figures indicate the number of cases found in the data file. They cannot be interpreted as summary statistics of the population of interest.