4) The role of neurotransmitter systems. Neurotransmitters carry information within the brain and from the brain to all the parts of the body. Gender differences have been found in the serotonin and noradrenalin systems. Serotonin release underlies the process of learning and consciousness. Carter reports that the ageing process in some serotonin systems might be more obvious in women than men, and there may be a link between serotonin disturbance, appetite, weight gain and depressed moods in women. Noradrenalin is released from the adrenal glands during stress. Low levels are related to poor concentration and depression.

5) Social roles. The theory here is that women’s roles in society contribute to depression. Their work is less valued than men’s, they have less power, less freedom to choose roles. Having young children in the house makes women more prone to depression. Research has backed this up. It also indicates that single women are less vulnerable to depression than single men, and married women more susceptible to it than married men. But married women are at low risk of depression in Mediterranean countries or in rural New Zealand homes, or if they’re British orthodox Jews. Carter notes the common factor: all value the home-making role.

6) Socialisation. When children are sex-stereotyped young, girls are vulnerable to depression and boys are resilient to it. Among girls, it’s thought to foster a sense of interdependence and concern for how they’re seen, and in boys one of mastery and control. Carter: “The way males and females are socialised from a young age in most western cultures is for young girls to be more nurturing, focused on relationships and looking after, and for boys to be independent.

“Those challenges are detrimental to women when it comes to living with most of the challenges in your life.”

7) Response style: women may be more likely than men to brood over depressive symptoms because they’re, well, women. One researcher suggests that “being emotional and inactive are part of the feminine stereotype”, just as ignoring mood and getting on with life are part of the masculine one. Carter’s summary of research: the more you mull it over, the more depressed you become.

“When women are depressed,” she says, “they tend to ruminate more, think about why they’re depressed – is it their fault or someone else’s – and analyse it. Men do more distracting things, such as drinking or picking up a hammer or whacking a ball. And the research is showing that that might be a better way of doing things. It goes against one view of psychotherapy, that if you’re depressed you need to talk about it, focus on it. But what happens is that people get depressed about being depressed.

“Meaning not everyone needs to do psychotherapy. Sometimes maybe the best thing to do is just get on with it. Ruminating is different. It gets dressed up as problem-solving. But it isn’t.”

8) Personality. Are relationships more critical to self-esteem in women than men, so that their self-esteem relies on the approval of others? Are women more likely to be unassertive, lack self-confidence and control over their lives, making them more prone overall to hopelessness and depression? These things may be true, but research on them is still inconclusive.

And there are other differences between men and women, too.