| Value | Category | 
                                    
                    
                        | 1 | More than 1 per mo | 
                                    
                    
                        | 2 | Once per month | 
                                    
                    
                        | 3 | Once each 2 mos | 
                                    
                    
                        | 4 | Once each 6 mos | 
                                    
                    
                        | 5 | Seldom | 
                            
            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.