| Value | Category | 
                                    
                    
                        |  | No | 
                                    
                    
                        | 1 | Yes | 
                                    
                    
                        | z | Not applicable | 
                                    
                    
                        | d | Inconsistency set to missing | 
                                    
                    
                        | a | Don't know | 
                                    
                    
                        | b | Refused to 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.