| Value | Category | 
                                    
                    
                        | 1 | 1. More than 6 years ago | 
                                    
                    
                        | 2 | 2. Between 3 and 6 years | 
                                    
                    
                        | 3 | 3. Less than 3 years ago | 
                                    
                    
                        | 9 | 9. Don t know | 
                            
            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.