| Value | Category | 
                                    
                    
                        | 1 | during last 15 days | 
                                    
                    
                        | 2 | 16 days to 365 days | 
                                    
                    
                        | 3 | more than 365 days ago | 
                                    
                    
                        | 4 |  | 
                                    
                    
                        | 9 |  | 
                                    
                    
                        | 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.