Jonathan Caspi in his book Sibling Agression wrote about “Scapegoating and disfavoritism” at page 195 which reads the following:
The fourth variation of favoritism involves families selecting one child to blame for family problems, or “scapegoating”. The scapegoated child is frequently accused of wrongdoing without merit. In families that scapegoat, there may not be any favored children, but one that is clearly disfavored. Disfavoritism involves a process where ‘parents single out one or more of their children for differential negative treatment’ and has been linked to problematic outcomes such as family conflict and increased shame in the disfavored child. Patterns of disfavoritism and scapegoating give tacit permission to siblings to mistreat the disfavored child. Practitioners should assess parental support of sibling agression toward children, particularly for those who are being consistently blamed without merit.