| Value | Category | 
                                    
                    
                        | 1 | no textbooks | 
                                    
                    
                        | 2 | only teacher has | 
                                    
                    
                        | 3 | share with two or more pupils | 
                                    
                    
                        | 4 | share with one pupil | 
                                    
                    
                        | 5 | by myself | 
                            
            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.