| Value | Category | 
                                    
                    
                        | 1 | Still in course | 
                                    
                    
                        | 2 | Participate in course in the past one year | 
                                    
                    
                        | 3 | Participate in course more than one year ago | 
                                    
                    
                        | 4 | Never | 
                                    
                    
                        | Sysmiss |  | 
                            
            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.