| Value | Category | 
                                    
                    
                        | 0 | ninguno/preescolar | 
                                    
                    
                        | 1 | primaria | 
                                    
                    
                        | 2 | secundaria | 
                                    
                    
                        | 3 | superior/univer. | 
                                    
                    
                        | 4 | alfabetizacion | 
                                    
                    
                        | 9 | no sabe / missing | 
                                    
                    
                        | Sysmiss |  | 
                            
            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.