| Value | Category | 
                                    
                    
                        | 1 | Nothing | 
                                    
                    
                        | 2 | In part | 
                                    
                    
                        | 3 | In great part | 
                                    
                    
                        | 4 | Fully/totally | 
                                    
                    
                        | 5 | No special qualifications | 
                                    
                    
                        | 6 | Refused to answer | 
                                    
                    
                        | 99 | N/R | 
                                    
                    
                        | 999 | N/A | 
                            
            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.