| Value | Category | 
                                    
                    
                        | 1 | yes, this visit only | 
                                    
                    
                        | 2 | yes, this and previous visit | 
                                    
                    
                        | 3 | yes, previous visit only | 
                                    
                    
                        | 4 | no | 
                                    
                    
                        | 8 | don't know | 
                            
            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.