| Value | 
                    Category | 
                                                                            
                                    
                    
                        | 0 | 
                        <12 months  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 1 | 
                        1 year  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 2 | 
                        2 years  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 3 | 
                        3 years  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 4 | 
                        4 years  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 5 | 
                        5 years  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 6 | 
                        6+ years  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 7 | 
                        Non-numeric  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 8 | 
                        Don't know  | 
                        
                            
                        
                        
                        
                        
                            
                    
                            
            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.