| Value | Category | 
                                    
                    
                        | 1 | 1. Fath=1, Moth=1 | 
                                    
                    
                        | 2 | 2. Fath=1, Moth>1 | 
                                    
                    
                        | 3 | 3. Fath>1, Moth=1 | 
                                    
                    
                        | 4 | 4. Fath>1, Moth>1 | 
                            
            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.