Birth Order, Family Size, and Schizophrenia

THE RELATIONSHIP of birth order to schizophrenia has been controversial. A few investigators of birth position in schizophrenic patients have reported increased numbers of cases who were firstborn or in the first half of the sibship,^1-3 whereas others found a preponderance of cases who were lastborn or in the second half of the sibship.^4-7 Several investigators, who were unable to discover any overrepresented birth position by means of the experimental methods which they employed, have concluded that birth positions were randomly distributed in schizophrenics.^8,9 A recent reviewer of birth order and its sequelae,¹⁰ while agreeing that birth order was related to other aspects of personality, dismissed the evidence on schizophrenia as being contradictory.

Apparent inconsistencies such as these may have discouraged earlier investigators from studying birth order more intensively¹¹; a more productive approach has been to study any variables which might obscure or modify the