| Value | Category | 
                                    
                    
                        | 1 | Neither able to read nor write | 
                                    
                    
                        | 2 | Able to read only | 
                                    
                    
                        | 3 | Able to write only | 
                                    
                    
                        | 4 | Uses braille | 
                            
            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.