| Value | Category | 
                                    
                    
                        | 1 | Less than 1 month | 
                                    
                    
                        | 2 | 1 to 5 months | 
                                    
                    
                        | 3 | 6 to 11 months | 
                                    
                    
                        | 4 | 1 to 2 years | 
                                    
                    
                        | 5 | 3 to 4years | 
                                    
                    
                        | 6 | 5 to 9years | 
                                    
                    
                        | 7 | 10 years or more | 
                                    
                    
                        | 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.