| Value | Category | 
                                    
                    
                        | 1 | normal day shift | 
                                    
                    
                        | 2 | evening or night shift | 
                                    
                    
                        | 3 | rotating shift with evening or night work | 
                                    
                    
                        | 4 | other work schedule | 
                                    
                    
                        | 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.