| Value | Category | 
                                    
                    
                        | -7 | na, not attempted (ran out of time) | 
                                    
                    
                        | 0 | incorrect or no response | 
                                    
                    
                        | 1 | correct | 
                                    
                    
                        | 9 |  | 
                                    
                    
                        | 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.