| Value | Category | 
                                    
                    
                        | 12 | 12 | 
                                    
                    
                        | 13 | 13 | 
                                    
                    
                        | 14 | 14 | 
                                    
                    
                        | 15 | 15 | 
                                    
                    
                        | 16 | 16 | 
                                    
                    
                        | 17 | 17 | 
                                    
                    
                        | 18 | 18 | 
                                    
                    
                        | 19 | 19 | 
                                    
                    
                        | 20 | 20 | 
                                    
                    
                        | 21 | 21 | 
                                    
                    
                        | -4 | Not asked | 
                                    
                    
                        | -3 | Not applicable | 
                                    
                    
                        | -2 | No answer | 
                            
            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.