| Value | 
                    Category | 
                                                                            
                                    
                    
                        | 1 | 
                        Before 1946  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 2 | 
                        In years 1946 -1960  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 3 | 
                        In years 1961 - 1980  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 4 | 
                        In years 1981 - 1995  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 5 | 
                        In years 1996 _ 2006  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 6 | 
                        After 2006  | 
                        
                            
                        
                        
                        
                        
                            
                    
                            
            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.