| Value | 
                    Category | 
                                                                            
                                    
                    
                        | 1 | 
                        Month and year - information complete  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 2 | 
                        Month and age - year imputed  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 5 | 
                        Year - age/month imputed  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 6 | 
                        Age - year/month imputed  | 
                        
                            
                        
                        
                        
                        
                            
                    
                            
            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.