| Value | Category | 
                                    
                    
                        | 1 | NATIONAL CENTER STAFF | 
                                    
                    
                        | 2 | TCH FROM SCH,BUT NOT TCH OF SELECTED CLS | 
                                    
                    
                        | 3 | TCH OF SELECTED CLS | 
                                    
                    
                        | 4 | OTHER | 
                                    
                    
                        | 9 | OMITTED | 
                                    
                    
                        | 11 | .A | 
                            
            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.