| Value | 
                    Category | 
                                                                            
                                    
                    
                        | 1 | 
                        Month and year  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 2 | 
                        Month and age  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 3 | 
                        Year and age  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 4 | 
                        Year  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 5 | 
                        Year, age and month imputed  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 6 | 
                        Age  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 7 | 
                        Month  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 8 | 
                        None  | 
                        
                            
                        
                        
                        
                        
                            
                    
                            
            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.