Of the seven quantitative studies identified in the review (3,14,17,20,28,32,35), two employed representative population survey methods. A study in the United Kingdom by Chakraborty and colleagues (3) that used a representative population-based sample compared 650 nonheterosexual participants with 6,811 heterosexual participants. Nonheterosexual participants were more likely to have probable psychosis (OR=3.75). A Netherlands population survey by Gevonden and colleagues (17) that employed two waves of data collection found increased rates of psychotic experiences among LGB (not including transgender or transsexual) participants in both waves, compared with the general population. In wave 1 (1996), among 115 LGB participants (76 men and 39 women), rates of reported psychotic experiences were greater (OR=2.56); this was also the case in wave 2 (2007–2009), with 114 LGB participants (58 men and 56 women) (OR=2.30). Further, among LGB participants, it was found that experiencing discrimination in the past year mediated 34% of the effect of LGB behavior on psychotic experience.

The remaining five studies used a range of survey-based methods (14,20,28,32,35). Two studies focused specifically on transgender individuals. Nuttbrock and colleagues (35), using structured, life course interviews with 571 male-to-female transgender participants in New York City, found that gender abuse (interpersonal abuse associated with gender identity) had a dose-response relationship with major depression and suicidality in adolescence, with less of an impact in later life. Cole and colleagues (14), employing a retrospective analysis of data from 435 clients assessed at a transgender clinic in Texas, found that nine individuals had diagnoses of bipolar disorder or schizophrenia, suggesting a rate of severe mental illness similar to that in the general population. A U.S. survey of 217 men and women who identified as bisexual revealed high rates of severe psychopathology, with 7% and 9%, respectively, reporting bipolar disorder and schizophrenia diagnoses (28). Furthermore, those with severe mental illness reported being less open about their sexual identity. A New Zealand survey of 561 lesbians conducted by Welch and colleagues (32) indicated a 3% rate of psychosis or schizophrenia; and among the 51 participants who had stayed in a psychiatric hospital, 42% perceived those settings as “antilesbian.” Finally, in a New York study by Hellman and colleagues (20) in which data for 68 LGBT individuals with severe mental illness were compared with data collected earlier from a sample of general outpatients, it was found that the diagnostic profiles of the groups were not significantly different nor were rates of hospitalization. However, LGBT participants had a mean age at onset of mental illness of 19.3 years, compared with 23.5 years in the control group.