| Value | Category | 
                                    
                    
                        | -9 | -9. Don't know | 
                                    
                    
                        | -8 | -8. Refused | 
                                    
                    
                        | -7 | -7. More than 10 years ago | 
                                    
                    
                        | -5 | -5. This year | 
                            
            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.