| Value | Category | 
                                    
                    
                        | 1 | Panel A - 2 Visits | 
                                    
                    
                        | 2 | Panel B 2 Visits | 
                                    
                    
                        | 3 | Panel A - Combined Visit | 
                                    
                    
                        | 4 | Panel B - Combined Visit | 
                                    
                    
                        | 5 | Panel A - Only Visit 1 | 
                            
            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.