Sex differences in concordance rates for schizophrenia: finding or artifact?

The literature on schizophrenia has reported a trend toward higher concordance rates for females in both monozygotic and dizygotic same-sexed twins. The validity of this finding is open to question. Rosenthal (1961 and 1962) pointed out that females are more likely than males to become inhabitants of chronic wards. Most of the studies reporting a sex difference used resident hospital populations. Gottesman and Shields (1972) noted that the sex difference disappeared when samples were based upon consecutive admissions. Sex differences have vanished in recent studies both as a result of changing research methods and the changing role of women in society.