Am J Psychiatry 1976; 133:1129-1133
Copyright © 1976 by American Psychiatric Association
A reconsideration of the Kety and associates study of genetic factors in the transmission of schizophrenia
LS Benjamin
The author reviews a study by Kety and associates that reported a
significantly greater prevalence of schizophrenic spectrum disorders among
the biological relatives of schizophrenic adoptees than among those of
nonschizophrenic adoptees. The principal statistical analysis of the Kety
study used an incorrect sample size (306 rather than 66) and failed to
weight each index and control case (family) equally. This violation of the
independence assumption would allow a few families to disproportionately
influence the outcome. The author argues that proper statistical analysis
applied separately to available categories indicates that significant
differences between the index and control groups occurred mainly in the
half-sibling category; this result violates the principle that genetic
effects increase with greater consanguinity. She concludes that Kety and
associates' study raises more questions than it answers regarding the role
of genetic factors in schizophrenia.
