| Value | Category | 
                                    
                    
                        | 1 | Less than 1 year ago | 
                                    
                    
                        | 2 | 1-2 years ago | 
                                    
                    
                        | 3 | >2-5 years ago | 
                                    
                    
                        | 4 | More than 5 years ago | 
                                    
                    
                        | 77 | Don't know | 
                                    
                    
                        | 88 | Refused | 
                                    
                    
                        | 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.