| Value | Category | 
                                    
                    
                        | 1 | Month and year - information complete | 
                                    
                    
                        | 5 | Year - month imputed, age calculated | 
                                    
                    
                        | 7 | Month - date placed | 
                                    
                    
                        | 8 | None - date placed | 
                                    
                    
                        | 9 | From calendar | 
                            
            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.