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Who is more likely to develop a mental illness: men or women? For the Victorians there was no doubt. After a visit to London’s St Luke’s Hospital for the Insane in 1851, Charles Dickens wrote:

The experience of this asylum did not differ, I found, from that of similar establishments, in proving that insanity is more prevalent among women than among men. Of the eighteen thousand seven hundred and fifty-nine inmates St Luke’s Hospital has received in the century of its existence, eleven thousand one hundred and sixty-two have been women.

But the Victorian view of female mental illness in both clinical and popular literature has long been critiqued for equating men with reason and women with madness, most famously by feminist critic Elaine Showalter, the author of Madwoman in the Attic. Such deeply embedded sexism means that women’s thoughts, feelings, and behaviour are misdiagnosed as insanity. And thus the “madwoman” remains securely locked in her attic.

No one, of course, wants to be accused of sexism. This might partly explain why today mainstream mental health professionals, psychologists, and psychiatrists give surprisingly little attention to the question of gender differences. And why the official line is that, though men and women vary in their vulnerability to particular types of mental illness, total rates are the same. The World Health Organization, for example, states: “Overall rates of psychiatric disorder are almost identical for men and women.”

But this is inaccurate. When you take a detailed look at the international epidemiological data, as we did when writing The Stressed Sex, the picture that emerges is very different – and pretty shocking. It turns out that in any given year total rates of psychological disorder are 20-40% higher in women than men.

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It’s true that men are more likely to develop problems with alcohol and drugs, and antisocial behavior is much more common among males than females. But that isn’t nearly enough to balance women’s significantly higher rates of all the most common psychological disorders, such as depression, anxiety, sleep problems, sexual problems, and eating disorders. For example, the National Comorbidity Survey Replication ­– a large, representative sample of the general US population – found that 9% of women and 5% of men had experienced depression in the previous twelve months, with a staggering 23% of women suffering from an anxiety disorder as compared to 14% of men.

Do these statistics capture genuine problems, or do they simply reflect the kind of sexism we described at the beginning of this article? Psychiatric classification is a controversial area – as you’ll have noticed if you followed the recent publicity surrounding the new edition of the Diagnostic and Statistical Manual, the so-called clinician’s bible. One might argue over the details of some diagnoses, but we’re in no doubt that these surveys tell the story of real distress, experienced by real people in search of help. This data isn’t illusory: it shows that huge numbers of people are struggling with psychological problems – and the majority of them are female. Some would say that men experience just as much mental illness as women: they just don’t admit it. But the scientific evidence to back up such an assertion simply isn’t there.

We don’t yet know why women suffer a from mental illness disproportionately. Maybe we’d see a little more urgency if it were men who were principally affected. Or perhaps the lack of attention reflects the relatively lowly importance of mental health: after all, physical illnesses that are predominately seen in women, such as breast cancer, have become major public health issues in recent years.

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What we do know is that social stresses make people vulnerable to mental illness, and research indicates that women’s roles may be especially demanding.Considering that on the whole women are paid less, find it harder to advance in a career, have to juggle multiple roles, and are bombarded with images of apparent female “perfection”, it would be amazing if there wasn’t some emotional cost. Women are also, of course, much more likely to have experienced childhood sexual abuse, a trauma that all too often results in lasting psychological damage.

A recent headline in the UK professional journal The Psychologist warned that “Studying sex differences is not for the faint-hearted,” and indeed we have personally encountered people who angrily reject the idea that women are experiencing more mental illness than men. But if we don’t face up to a problem we cannot hope to solve it. So let’s have the awkward discussions. Let’s prioritize research into the causes of mental illness and specifically the role that gender may play. And let’s end the discrimination, inequality, and downright misogyny that seem to be triggering profound psychological distress in so many women.