| Value | Category | 
                                    
                    
                        | 1 | less than 6 months ago | 
                                    
                    
                        | 2 | 6-11 months ago | 
                                    
                    
                        | 3 | 1-5 years ago | 
                                    
                    
                        | 4 | more than 5 years ago | 
                                    
                    
                        | 8 | don't know | 
                                    
                    
                        | 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.