| Value | Category | 
                                    
                    
                        | 1 | more than once a week | 
                                    
                    
                        | 2 | once a week | 
                                    
                    
                        | 3 | once a moth | 
                                    
                    
                        | 4 | 1-2 times a term | 
                                    
                    
                        | 5 | 1-2 times a year | 
                                    
                    
                        | 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.