Thought disorder in the relatives of schizophrenics. A meta-analytic review of selected published studies

Selected published studies investigating the existence of thought disorder in close relatives were re-examined in response to the conclusion by Saccuzzo, Callahan, and Madsen (J Nerv Ment Dis 176:368-371, 1988) that "the evidence for thought disorder in the families of schizophrenics is weak and inconclusive." A meta-analysis was performed on a subset of these studies to determine the (weighted) average effect size and its variability. The results indicated that the effect size was significant, i.e., there is a definite association between being related to a schizophrenic and manifesting (subclinical) thought disorder. Moreover, the variability of effect sizes among studies was not entirely due to sampling error and needs to be explained in terms of moderator variables.