| Value | Category | 
                                    
                    
                        | 0 | I do not take extra tuition | 
                                    
                    
                        | 1 | Once a month | 
                                    
                    
                        | 2 | 2 or 3 times per month | 
                                    
                    
                        | 3 | Once or twice per week | 
                                    
                    
                        | 4 | 3 or more times per week | 
                            
            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.