| Value | Category | 
                                    
                    
                        | 1 | One year or less | 
                                    
                    
                        | 2 | Two to five years | 
                                    
                    
                        | 3 | Five to nine years | 
                                    
                    
                        | 4 | Ten to nineteen years | 
                                    
                    
                        | 5 | Twenty years or more | 
                                    
                    
                        | 8 |  | 
                                    
                    
                        | 9 | 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.