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From "Sexual Orientation and Psychiatric Vulnerability: A Twin Study of Neuroticism and Psychoticism" (2011):

Abstract

Recent evidence indicates that homosexuals and bisexuals are, on average, at greater risk for psychiatric problems than heterosexuals. It is assumed with some supporting evidence that prejudice often experienced by nonheterosexuals makes them more vulnerable to psychiatric disorder, but there has been no investigation of alternative explanations.

[...]

We found significant genetic correlation between sexual orientation and both Neuroticism and Psychoticism, but no corresponding environmental correlations, suggesting that if there is a common cause of both nonheterosexuality and psychiatric vulnerability it is likely to have a genetic basis rather than an environmental basis.

Is this a valid study?

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    possibly related: en.wikipedia.org/wiki/… – yms Oct 13 '17 at 2:22
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    Roughly the same set of authors have published more studies like that (with different samples): doi.org/10.1017/S0033291711001577 Their conclusion in the abstract of the latter study is a bit more reserved, stated as "causality cannot be definitively resolved". Nevertheless, they also wrote that "genetic factors accounted for a majority (60%) of the correlation between sexual orientation and depression". – Fizz Oct 13 '17 at 10:02
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    Other studies failed to even find an association: ncbi.nlm.nih.gov/pubmed/28252373 So YMMV. You'll want to look for some review article on this topic (if it exists). – Fizz Oct 13 '17 at 10:11
  • I'm assuming you referring to the latter one (because I quoted from the former). So here's a quote from that one too: "After adjusting for known risk factors for depression, there was no difference in prevalence of past 12-month or lifetime major depressive episode between sexual minorities and heterosexuals." – Fizz Oct 14 '17 at 2:11
  • And after a bit more reflection, I think you have misrepresented the paper in your title a little bit, because non-heterosexual does not equal homosexual. – Fizz Oct 15 '17 at 1:01
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Summary: The claimed paper is a real scientific study that follows the norms and standards of science. In a direct response to this article, a peer scientist criticizes the methods and conclusions of the claimed paper. I am not qualified to sort out which of them is correct, but the criticisms seem valid to me.

This is definitely not a settled scientific question.


Background on the claim

The paper in the claim, which I will refer to as the claim paper, finds that homosexuals score higher on "Eysenck’s orthogonal personality scales Neuroticism and Psychoticism." The claiming paper cites scientific articles that find that these measures are correlated with depression, anxiety, schizophrenia and other psychotic disorders, antisocial behavior and conduct problems, and suicidal behavior.

The paper goes on to conclude that there may be a genetic basis that causes both neuroticism and psycopathy as well as homosexuality.

The claiming paper does not look at mental illness directly, nor does it sequence anyone's genes or look at genetic markers.

This followup paper by the same authors, makes a much more clear claim about a genetic cause.


Do the results of this study match the results of other studies in the scientific literature? To answer this, I began by reading the articles reviewed in this article's introduction.

A. This meta-analysis read 25 different studies on homosexuality and mental health. The 25 different studies collectively found that homosexuals were more at risk for depression, anxiety, and suicide attempts as well as drug and alcohol abuse.

B. This study finds that homosexuals reported "more childhood psychological and physical abuse by parents or caretakers, more childhood sexual abuse, more partner psychological and physical victimization in adulthood, and more sexual assault experiences in adulthood. Sexual orientation differences in sexual victimization were greater among men than among women." These things have been linked to a greater severity of mental illness, and are not genetic as the claim paper believes.

C. This section from the intro to the claim paper summarizes findings from other studies have found similar results to the claim paper.

Bozkurt et al. (2006) found in a sample of Turkish men that homosexuals scored significantly higher on Psychoticism (as well as nonsignificantly higher on Neuroticism) than a matched heterosexual control group and Eisinger et al. (1972) found that homosexual women scored significantly higher than Neuroticism norms. In a small study, however, Wilson (1982) found that homosexual women scored lower than heterosexual women.

Literature Summary: Many other papers find a link between homosexuality and mental illness, although most of these attribute this to environmental factors, like abuse or victimization. A few other papers find a link between homosexuality and neuroticism/psycopathy, but I did not see a claim that there is a genetic causal claim. The claim paper seems to be the first to say that.


I skimmed a number of the articles that cite the claim paper articles and found that most of them cited the claim paper indifferently. They repeated the results but do not editorialize about this study's quality. Then I found this open letter that criticizes the methods and conclusions of this paper. They list three concrete objections. The easiest to understand, and most directly related to the claimed study is quoted below. (Emphasis mine)

Zeitsch et al. (2011) defined participants as non-heterosexuals if they described their sexual feelings as anything other than “exclusive attraction to the opposite sex.” The majority (59%) of non-heterosexuals in this sample scored a 1 on the Kinsey Scale, describing themselves as “predominantly heterosexual, only incidentally homosexual.” The study found that people who reported exclusive heterosexuality were less likely to be neurotic than those who reported other values (although the relationship was markedly non-linear: the lowest average neuroticism of all groups was among people who reported a Kinsey score of 4). The study then reported an r of 0.25 between the inferred (via a bivariate Cholesky decomposition) genetic predictors of sexual orientation and genetic determinants of neuroticism. In their second study,Zeitsch et al. (2012) found evidence of shared genetic causes of depression and non-heterosexuality. However, this study also found that depression and non-heterosexuality shared environmental causes, namely, sexual abuse in childhood and risky childhood family environments. These findings would appear to support, rather than refute, our own conclusions.

This is an accurate description of the methods of the claim paper.

We operationally defined those with any degree of sexual attraction to the same sex (Kinsey scores 1–6) as nonheterosexuals, and the associated trait as nonheterosexuality.

I personally have a hard time with any scientific study that considers completely gay men to be the same as men who have occasional gay thoughts, but are other wise straight. The fact that this represents most of the men in the study seems pretty damning to me.

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    Since the OP challenged my reading comprehension, I looked up another paper by Scott et al., which says "Gay men reported lower levels of depressive symptoms than heterosexual men." (Emphasis mine.) I don't have enough interest to dig into this topic further, but it seems some of results are not reproducible with different operational definitions. (Either that or gay Canadians are much happier than gays elsewhere such studies were conducted.) – Fizz Oct 15 '17 at 0:36
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    However, the same source reported that "men who reported having sex with men were five times more likely to report depressive symptomatology compared to men who reported opposite sex partners." So yeah, there's probably something in that distinction that matters. The main conclusion of this study was however that "Sexual orientation was not a significant independent predictor of depressive symptoms overall." It's possible the Scott study didn't have enough power (sample size), although it was 6 times larger than the Bailey ones. – Fizz Oct 15 '17 at 0:41
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    If you look at the publication dates, that's impossible. The Scott papers are from 2016-2017, whereas the meta-analysis you found is from 2008. By the way, the Scott papers were the first hits in pubmed, that's the only reason I found them. Also, the meta-analysis studied LGB as a group. – Fizz Oct 15 '17 at 1:18
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    Given that there are obvious potential environmental issues which could lead to issues with depression & suicidal thought, specifically cultures which do not accept homosexuality and may villanize or even attack people who are homosexual, I'm curious how the study could prove a genetic factor. How can one control for such a large potential environmental influence and still be confident of a genetic one? – dsollen Oct 16 '17 at 21:51
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    @dsollen I pretty much agree. Like every other effect in the universe, something causes homosexuality, and that thing may cause other things. Figuring out what that cause is has proven tricky. On the other hand, jumping to conclusions based on limited evidence is dead simple. – BobTheAverage Oct 16 '17 at 22:31

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