| Value | Category | 
                                    
                    
                        | 1 | None | 
                                    
                    
                        | 2 | 1 yr. | 
                                    
                    
                        | 3 | 2 yrs. | 
                                    
                    
                        | 4 | 3 yrs. | 
                                    
                    
                        | 5 | 4 yrs. | 
                                    
                    
                        | 6 | 5 yrs. | 
                                    
                    
                        | 7 | 6 yrs. | 
                                    
                    
                        | 8 | 7 yrs and over | 
                                    
                    
                        | 9 | Not stated | 
                                    
                    
                        | 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.