| Value | Category | 
                                    
                    
                        | 0 | not applicable | 
                                    
                    
                        | 1 | 3 months | 
                                    
                    
                        | 2 | 4-6 months | 
                                    
                    
                        | 3 | 7-9 months | 
                                    
                    
                        | 4 | 10-12 months | 
                                    
                    
                        | 5 | 13 months or more | 
                                    
                    
                        | 9 | no answer | 
                            
            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.