| Value | Category | 
                                    
                    
                        |  | NIU (not in universe) | 
                                    
                    
                        | 1 | Yes | 
                                    
                    
                        | 2 | No, not specified | 
                                    
                    
                        | 3 | No, attended in the past | 
                                    
                    
                        | 4 | No, never attended | 
                                    
                    
                        | 9 | Unknown/missing | 
                            
            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.