| Value | Category | 
                                    
                    
                        | -9 |  | 
                                    
                    
                        | -7 | na | 
                                    
                    
                        | 0 | incorrect or no response | 
                                    
                    
                        | 1 | correct | 
                                    
                    
                        | 2 | point at correct (but couldn't say number) | 
                                    
                    
                        | 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.