| Value | Category | 
                                    
                    
                        | 1 | a written contract, decision, license, etc | 
                                    
                    
                        | 2 | oral contract with employer | 
                                    
                    
                        | 3 | without a contract | 
                                    
                    
                        | 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.