| Value | Category | 
                                    
                    
                        | 1 | Very useful | 
                                    
                    
                        | 2 | Somewhat useful | 
                                    
                    
                        | 3 | Just a little useful | 
                                    
                    
                        | 4 | Not useful at all | 
                                    
                    
                        | 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.