| Value | Category | 
                                    
                    
                        | 1 | internal qc only | 
                                    
                    
                        | 2 | external qc only | 
                                    
                    
                        | 3 | both, internal and external qc | 
                                    
                    
                        | 4 | send slide for re-reading | 
                                    
                    
                        | 6 | other | 
                            
            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.