| Value | Category | 
                                    
                    
                        | 1 | regular, every month | 
                                    
                    
                        | 2 | periodical, 5 - 6 times a year | 
                                    
                    
                        | 3 | rare, 1 - 2 times a year | 
                                    
                    
                        | 4 | seasonal | 
                                    
                    
                        | 99889988 | refusal | 
                                    
                    
                        | 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.