| Value | Category | 
                                    
                    
                        | -1 | missing | 
                                    
                    
                        | 0 | never | 
                                    
                    
                        | 1 | just once or twice | 
                                    
                    
                        | 2 | several times | 
                                    
                    
                        | 3 | many times | 
                                    
                    
                        | 4 | always | 
                                    
                    
                        | 9 | don't know | 
                                    
                    
                        | 998 | refused | 
                            
            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.