| Value | 
                    Category | 
                                                                            
                                    
                    
                        | -99 | 
                        Don't know  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | -96 | 
                        Other  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | -95 | 
                          | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | -90 | 
                        Not specified by interviewer  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 0 | 
                          | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 1 | 
                        Day  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 2 | 
                        Trip  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 3 | 
                        Barrel/gallon  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 4 | 
                        Week  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 5 | 
                        Month  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 6 | 
                        Year  | 
                        
                            
                        
                        
                        
                        
                            
                    
                                    
                    
                        | 7 | 
                        Container  | 
                        
                            
                        
                        
                        
                        
                            
                    
                            
            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.