| Value | Category | 
                                    
                    
                        | 1 | At least once or twice a week | 
                                    
                    
                        | 2 | less than once a week | 
                                    
                    
                        | 6 | not applicable | 
                                    
                    
                        | 8 | not admin. | 
                                    
                    
                        | 9 | missing | 
                            
            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.