| Value | Category | 
                                    
                    
                        | 1 | One week | 
                                    
                    
                        | 2 | One month | 
                                    
                    
                        | 3 | Three months | 
                                    
                    
                        | 4 | Six months | 
                                    
                    
                        | 5 | One year | 
                                    
                    
                        | 6 | Other | 
                                    
                    
                        | 7 |  | 
                                    
                    
                        | 8 |  | 
                                    
                    
                        | 9 |  | 
                                    
                    
                        | 10 |  | 
                                    
                    
                        | 11 |  | 
                                    
                    
                        | 12 |  | 
                                    
                    
                        | 99 |  | 
                                    
                    
                        | 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.