| Value | Category | 
                                    
                    
                        | 1 | No difficulty | 
                                    
                    
                        | 2 | Some difficulty | 
                                    
                    
                        | 3 | A lot of difficulty | 
                                    
                    
                        | 4 | Unable to do | 
                                    
                    
                        | 5 | Do not know | 
                                    
                    
                        | 8 | Not applicable | 
                                    
                    
                        | 9 | Unspecified | 
                            
            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.