Fifty-seven siblings were less entangled in the family emotional life than 30 schizophrenic patients in the same families. Level of illness in siblings was associated with the degree of family entanglement. It appears, however, that the percentage of these siblings at various levels of illness may not differ from proportions to be found among young persons in the general population. No correlation could be found between the patient's rank order of health and that of siblings in the same family. The siblings did not fit a single pattern in personality, but fell into several clusters which were characterized by different survival styles within the family of origin.
Hoover CF, Franz JD. Siblings in the Families of Schizophrenics. Arch Gen Psychiatry. 1972;26(4):334–342. doi:10.1001/archpsyc.1972.01750220044009