| Value | Category | 
                                    
                    
                        | 1 | 1. Mth & yr given | 
                                    
                    
                        | 2 | 2. Yr given, DK mth | 
                                    
                    
                        | 3 | 3. Mth given, DK yr | 
                                    
                    
                        | 8 | 8. DK year & mth | 
                                    
                    
                        | 9 | 9. Miss | 
                                    
                    
                        | Sysmiss |  | 
                            
            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.