| Value | 
                    Category | 
                                    
                                                        
                        | 0 | 
                        Never | 
                                            
                                                        
                        | 1 | 
                        0-11 months ago | 
                                            
                                                        
                        | 2 | 
                        12+ months ago | 
                                            
                                                        
                        | 3 | 
                        Yes, but don't remember when | 
                                            
                                                        
                        | 4 | 
                        Yes, but frequency in last 12 months 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.