| Value | Category | 
                                    
                    
                        | 1 | I have never smoked | 
                                    
                    
                        | 2 | I have not stopped smoking | 
                                    
                    
                        | 3 | 1-3 months | 
                                    
                    
                        | 4 | 4-11 months | 
                                    
                    
                        | 5 | One year | 
                                    
                    
                        | 6 | 2 years | 
                                    
                    
                        | 7 | 3 years or longer | 
                                    
                    
                        | 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.