| Value | Category | 
                                    
                    
                        | 1 | 1. Yes | 
                                    
                    
                        | 3 | 3. No | 
                                    
                    
                        | 4 | 4. Not probed | 
                                    
                    
                        | 6 | 6. N/A | 
                                    
                    
                        | 7 | 7. Refuse | 
                                    
                    
                        | 8 | 8. DK | 
                                    
                    
                        | 9 | 9. Miss | 
                                    
                    
                        | 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.